1. The interstate speed limit for cars is 75 miles per hour in Nebraska, Nevada, and New Mexico,Oklahoma, South Dakota, Utah, and Wyoming and is the highest in the United States. To discourage passing, minimum speeds are posted, so that the difference between the fastest and the slowest moving traffic is no more than 20 miles per hour. Therefore the speed x of a car must satisfy the inequality 55 <= x >= 75.

2. Linear equation of two variables:

. . .y = (1/2)x

. . .y = (-3/4)x + 5

. . .6x - y = 10

. . .y = (-3/4)x - 1

I know that that have to substitute:

. . .6x - ((-3/4)x - 1) = 10

. . .6x + (3/4)x + 1 = 10

. . . . . . . . . . . . .-1. . .-1

. . .(6 + 3/4)x = 9

But I know that I have done something that is incorrect.

4. Interest: A man invests $2200 in three accounts that pay 6%,8%, and 9% annual interest, respectively. He has three times as much invested at 9% as he does at 6%. If his total interest for the year is $178, how much has he invested?

5. Filling a Pool: A pool can be filled by an inlet pipe in 8 hours. The drain will empty the pool in 12 hours. How long will it take to fill the pool if both the inlet pipe and the drain are open?