A proton (mass 1 u) is shot toward an unknown target nucleus at a speed of 2.5 X 10^6 m/s. The proton rebounds with its speed reduced by 25% while the target nucleus acquires a speed of 3.12 x 10 ^5 m/s. What is the mass, in atomic mass units , of the target nucleus?

This is what I did:

(1) (2.5*10^6) + (m)(0) = (1) ( 6.25 * 10^5) + (m) (3.12 * 10^5)
6.01u = m

Is this correct??