8th grade write and solve the equation

Question

Selma packs one box in 5 minutes and has already packed 12 boxes.  Lynn packs one box in 7 minutes and has already packed 18 boxes. How many more minutes does each need to work in order to have packed the same amount of boxes?

Answer 1

Selma is 1/5 box per minute and Lynn is 1/7 box per minute

12 + (1/5) t = 18 + (1/7) t

Multiplies everything by 35:

420 + 7t = 630 + 5t

420 + 2t = 630

2t = 210

t = 105

After 105 minutes...

Selma will have packaged 12 + 105/5 = 12 + 21 = 33 boxes

Lynn will packages 18 + 105/7 = 18 + 15 = 33 boxes

105 minutes =

1 hour and 45 minutes =

1.75 hours