Test 2 Section 4 #34 Thanks!!

Let’s say that d = the number of hours Doug spent in the lab, and l = the number of hours that Laura spent in the lab. Here are the equations we can write from the question:

l + d = 250
d = l + 40

This question is begging for a little substitution. Let’s take the expression for d we have in the second equation and plug it into the first.

l + (l + 40) = 250
2l +40 = 250
2l = 210
l = 105