A stocker put 57 boxes of detergent on the shelves in 2 minutes. After 5 minutes, he had put 117 boxes on the shelves. How many boxes were on the shelves when he started?

(2,57) (5,117)

slope = (117 - 57) / (5 - 2) = 60/3 = 20

y = mx + b

slope (m) = 20

(2,57) ... x = 2 and y = 57

sub and find b, the y int

57 = 20 (2) + b

57 = 40 + b

57 - 40 = b

17 = b

equation is : y = 20x + 17 ... with x being the number of minutes, and 17 being the number of boxes on the shelf when he started

57 boxes of detergent on the shelves in 2 minutes

After 5 minutes, he had put 117 boxes on the shelves

117 - 57 = 60 (60 boxes of detergent for 3 minutes)

60/3 = 20 (20 boxes of detergent per minute)

so

20 x 5 = 100 boxes of detergent

117 - 100 = 17 boxes

answer

17 boxes of detergent were on the shelves when he started