a) v=dx/dt, r=acceleration
t=ax2+bx
differentiating wrt t
1=2ax*(dx/dt)+b(dx/dt)
2avx+bv=1
x=(1-bv)/2av
again differentiating wrt t
2a(v(dx/dt)+x(dv/dt))+b(dv/dt)=0
2a(v2+rx)+br=0
2arx+br=-2av2
(2ax+b)r=-2av2
if answer is independant of x
then from above
(2a((1-bv)/2av)+b)r=-2av2
simplify to get answer