One day a store sold 29 sweatshirts. white ones cost $11.95 and yellow ones cost $11.50. in all, $338.90 worth of sweatshirts were sold. how many of each color were sold?

A) W + Y = 29
B) 11.95 W + 11.50 Y = 338.90

Multiply equation A by -11.5
A) -11.5 W + -11.50Y = -333.50 then add to B)
B) 11.95 W + 11.50 Y = 338.90

.45 W = 5.4
 W = 12 and so
Y = 17