It says two laps. So you can assume that you have 1 lap = to a distance of 1s, and two laps = to a distance of 2s.

For the full two laps:

x(distance) = 2s

u = 0 m/s

v = 15 m/s

a = a

For 1 lap:

x = s

u = 0

v = v

a = a

For lap no. 1:

v^2 = u^2 + 2as

v^2 = 0^2 + 2as

= 2as

For lap no. 2:

v^2 = u^2 + 2as

225 = 0^2 + 2*a*2s = 4as

therefore, 4as = 225 and 2as = 225/2

v^2 = 2as = 225/2

v = sqrt(225/2) ~ 10.6 ~ 11 m/s