Okay, have you learned about linear equations?
It's in the form:
y = mx + c
This is the equation of a line on cartesian plane (coordinates system/grid)
where y is a variable (usually a dependent variable, if you don't know what that means, it's okay)
x is an independent variable (same here, but it's just like an opposite of y)
m is a gradient or slope and determines how fast the line climbs up or down.
c is a y-intercept, which means where the line meets the y-axis.
In your problem, you are given for company A giving $25 per month and a rate of $0.22 per minute of call. The $25 is a constant and you have to pay that amount regardless of how much time you spend on calls. The $0.22 is another constant. You will have to pay $0.22 for every additional minute you use, no more, no less. But what happens here is that the more you make calls, the larger the total amount will be.
This can be written as:
y = 0.22x + 25
Let's see. If you don't make any call, you will have to pay $25, right?
So, y = 0.22(0) + 25 = 0 + 25 = 25
What I did is understand that y gives the total money I have to pay if I make no call at all and x is the number of minutes I spend on calls. Similarly, having 1 minute of call means I have to pay $0.22 on top of $25, right?
y = 0.22(1) + 25 = $25.22
That's exactly it!
So, I can take any value of x in that equation and the resulting y that I calculate will give me the total fees I'll have to pay company A. Can you try to make the equation for company B?