Answer
1.2 hours
Work Step by Step
Carlos started his homework 12 minutes early. In 60 minutes, he can get 25 problems done, so in 12 minutes, he can get 5 problems done. This expression represents how many problems he gets down after $x$ hours from when Cecelia started her homework
$25x + 5$
Cecelia had no head-start and can do 30 problems an hour. This expression represents how many problems Cecelia did $x$ hours from when Cecelia started her homework
$30x$
Equate them and solve
$25x+5 = 30x$
$5 =5x$
$x = 1$
The question is asking how long after Carlos started would they have the same number of problems done. Carlos started $0.2$ hours early, so the answer is $1 + 0.2$
or just $1.2$ hours.
