Answer:
35 mph
Explanation:
time = distance / speed
210 miles and has an average of a certain speed
t = 210 / s
If the average speed had been 3mph more, he could have traveled 228 miles in the same length of time
t = 228 / (s + 3)
Set equal
210 / s = 228 / (s + 3)
Cross multiply
210s + 630 = 228s
Subtract 210s from both sides
630 = 18s
Divie both sides by 18
35 = s
35 mph