A31.5 kg shell is fired from a 2,100 kg cannon with a velocity of 500 m/s. what is the resulting velocity of the cannon

We know, m1v1 = m2v2
Here, m1, v1 = mass & velocity of cannon
m2, v2 = mass & velocity of shell

2100 * v1 = 31.5 * 500
v1 = 15750 / 2100
v1 = 7.5 m/s

In short, Your Answer would be 7.5 m/s

Hope this helps!

The answer is  a.first and third quarters