8th Grade math question

Question

Natalia bought 3 boxes of pencils and 9 reams of paper for $75. Ronnie bought 8 boxes of pencils and 5 reams of paper for $67. Set up and solve a system of equations by elimination to determine the cost of a box of pencils and a ream of paper.

Answer 1

3b + 9r = 75

8b +5r = 67

15b + 45r = 5(75) = 375

72b + 45r = 9(67) = 603

subtract

72b-15b = 603-375

57b = 228

b = 228/57 = 4 boxes of pencils

5r = 67-8b =67-32 = 35

r =35/5 = 7 reams of paper

3(4)+9(7) = 12+63 = 75

8(4)+5(7) = 32+35 = 67

4 boxes of pencils and 7 reams of paper