Let x be the speed of Jack.
Then the distance Jack traveled during 2 hours was 2x.
Jill traveled 80 miles more, so she traveled (2x+80) miles.
Her speed was (x+10) miles per hour.
She spent 3.5 hours, hence
3.5*(x+10) = 2x + 80.
Solve the equation
3.5x + 35 = 2x + 80
3.5x - 2x = 80 - 35
1.5x = 45
x = = 30 miles per hour was the Jack' speed. ANSWER