Question 818258
That is a physics problem, and you do not have enough information.
You could apply conservation of momentum and conservation of energy if there is no braking.
{{{M*V[i]=M*V[f]+m*20}}}
{{{M*V[i]^2/2=M*V[f]^2/2+m*20^2/2}}}
where
{{{M}}}=mass of moving car
{{{m}}}= mass of stopped car
{{{V[i]}}}= initial speed of moving car
{{{V[f]}}}= final speed of moving car after the collision
However, you do not know the masses of the cars.
I do not think it can be solved without further information, but I am going to review my physics course to see if and what additional information would be needed.
Was it a fully inelastic collision, where both cars ended up moving together as one so {{{V[f]=20}}}?
Or were they bumper cars, and it was a fully elastic collision?