Answer:
x = 5
Explanation:
Distance travelled in 2 secs at a speed of x ms-1
= speed * time = 2x m.
Distance travelled at (3x - 14) ms-1 for x secs
= x(2x - 14) m.
Therefore 2x + x(3x - 14) = 15
3x^2 - 12x - 15 = 0
x^2 - 4x - 5 = 0
( x - 5)(x + 1) = 0
x = 5, -1
As x cannot be negative it must be 5