From the first look, we can see the question states the car is undergoing constant acceleration, thus we know the SUVAT equations are valid. Then reading on, we're required to find the final velocity, v, of the car as it passes B, therefore we must find at least 3 of the 4 other variables of the system (a, u, t and S in addition to v). As we are given a = 2ms^-2, u = 10ms^-1 (the velocity at A) and S = 50m, we can put these values straight into any SUVAT equation containing a, u, v and S. This equation is v^2 = u^2 +2as. Therefore the answer is:
v = sqrt(u^2 + 2as)v = sqrt(10^2 + 2250)v = 10*sqrt(3) = 17.32 ms^-1 to 2 d.p