This is a proportion problem. Examples are: (1) comparing dimensions on a map or a blueprint to real dimensions, (2) making more food than a recipe indicates, (3) determining the behavior of a real airplane from an experiment conducted in a wind tunnel [except that, here some values are squared], ...
The very most important item with proportions is to keep the units the same on both sides of an equation. Since this problem doesn't have units, I'll take the liberty of assigning them (because I can't solve the problem otherwise):
"if 100 inches equals 78.85 miles, then what equals 35 miles?"
O.K., now I feel better.
100 inches / 78.85 miles = x inches / 35 miles
78.85x = 3500 [cross-multiply; we can drop units now, I'm fine]
x = 44.39 (rounded)
(note: 100 is a bit bigger than 78.85 and 44.39 is a bit bigger than 35)