Velocity of balls

Question

Two balls start at the same instant and move slowly along the same straight line. The first and second balls have a displacement of B1 and B2 metres resp. 

 

What time will they have the same velocity? Assumption? 

 

 

=B₁ = 1/3 (x³ + 6x² + 12x + 8)

 

B2 = 5x² - 5x + 6

Answer 1

B1 = 1/3 (x^3 + 6x^2 + 12x + 8)

B2 = 5x^2 - 5x + 6

dB1/dt=v1=x^2+4x+4 (1)

dB2/dt=v2=10x-5 (2)
(1)=(2)
x^2+4x+4= 10x-5
x^2-6x+9=0
x=3
v1,v2=25