The product of two numbers is 800.  The difference between the numbers is 20.  What are the two numbers?

A 9 inch apple pie sells for $6.  What is the cost per square inch rounded to the nearest cent?

The function d(t) = 17t² - 110t gives the distance a car going a certain speed will skid in t seconds.  Find the time it would take for the car to skid 180 feet.

Put the equation y = x² - 8x + 7 in the form y = (x - h)² + k

The hypotenuse of a right triangle is 16 ft long.  One leg is 6.6 ft longer than the other leg.  Find the lengths of the legs.  Round to one decimal place.

12x -2y = 6 , a dilation centered at the origin with a scale factor of 4 is applied to the line.  What is the slope
and y-intercept after the dilation?

How many copies can be made in 3 minutes and 30 seconds, when you can make 32 copies per minute?

Can you explain to me how to solve the following problem?

Isaac bought school shirts for $35 each and school pants for $49 each. If he buys 9 items and his total cost is $357, how many shirts did he buy?

I solved it with trial and error, but I know there is an algebraic method. 

Thank you.