# Make k the subject of an equation - no answers please, just direction

#### Luffy

##### New member
I have read my tutorial book over and over but i still cannot understand how to make k the subject of the below equation.

I really need to understand how this works so please do not give me any answers - just direct me and explain where I go wrong.

The question asks I make k the subject of;

t= 9s/5+4k

I begin by multiplying both sides by (5+4k) giving

t*(5+4k) = 9s/5+4k*(5+4k)

Simplifying gives me

t(5+4k)=9s (i think)

multiplying both sides gives me

5t+4kt=9s

I want to find all the terms that contain the required subject, k, and move them to the left.

4kt=5t+9s

Now i want to subtract and then divide by t which gives

k=5t-9s/4t

Im stabbing in the dark with parts of this equation. Any direction would be appreciated

#### Ishuda

##### Elite Member
I have read my tutorial book over and over but i still cannot understand how to make k the subject of the below equation.

I really need to understand how this works so please do not give me any answers - just direct me and explain where I go wrong.

The question asks I make k the subject of;

t= 9s/5+4k

I begin by multiplying both sides by (5+4k) giving

t*(5+4k) = 9s/5+4k*(5+4k)

Simplifying gives me

t(5+4k)=9s (i think)

multiplying both sides gives me

5t+4kt=9s

I want to find all the terms that contain the required subject, k, and move them to the left.

4kt=5t+9s

Now i want to subtract and then divide by t which gives

k=5t-9s/4t

Im stabbing in the dark with parts of this equation. Any direction would be appreciated
Before we start on making k the subject of the formula, I should remind you that formulas sometimes need parentheses and, according to your workings, this is one of those times. That is, you equation is
t = 9s / (5+4k)
not
t= 9s/5 + 4k.

That said, you need to put k on the left hand side by itself. You are correct up to
5t + 4kt = 9s
but, subtracting 5t from both sides gives
4kt = 9s - 5t
not what you have. Your statement of dividing by t [actually 4t] is also correct but, as before, you will need some punctuation (parentheses) to format the answer correctly.