Tony and sal drove in opposite direction from the same starting point. tony averaged 15 mpg faster then sal. after 5 hours they were 425 miles apart. how fast was each of them driving?

You meant "15 mph, faster" not "15 mpg faster", right?

distance = speed * time

distance = 425 miles
time = 5 hours
Sal's speed = s
Tony's speed = s + 15

Since they drove in opposite directions, the speed between them is the sum of the speeds.

distance = speed * time
425 = (s + s + 15) * 5
85 = 2s + 15
70 = 2s
s = 35

s is Sal's speed and is 35 mph.
Tony's speed is 15 mph faster, so Tony's speed = 35 mph + 15 mph = 50 mph

Sal's speed was 35 mph
Tony's speed was 50 mph