I got a version of the snow plow problem for differential equations but I can't seem to solve it for the life of me. I looked at some solutions online and had trouble comprehending them. If some one could give me a hand it would be much appreciated.

The problem: One day snow began to fall before dawn and continued to fall at a constant rate. At 6AM a road crew set out to clear the roads. By 7AM they had cleared 5 miles. By 8AM they had cleared and additional 3 miles. When did the snow begin to fall.

What I've written so far:

I can't for the life of me figure out how to solve the system of equations that I've gotten. Thanks in advance for the help.