Answer: u=(mv-ft)/m
Step-by-step explanation: f=m(v-u)/t
Multiply both sides of the equation by t
f×t = m(v-u)/t ×t 
Simplifying, ft = m(v-u) 
Expanding the brackets, 
ft = mv-mu
By transfer of terms, 
mv - ft = mu
Dividing both sides by m, 
(mv-ft)/m = u
Hence, u= (mv-ft)/m