You basically make an equation out of this and set the two expressions equal to each other.
Let x equal the number of hours where the snowfall will be equal in both towns.
In town one, the amount of snowfall can be written as 2+6x. In town two, the amount of snowfall can be written as 7+3x.
So to find when they will be equal, set them equal and solve:
2+6x=7+3x
3x=5
x=5/3 or 1 2/3 hours. In minutes, this is 100 minutes.