use your answer to (b) to help calculate the mass and the velocity of the ball

Question

that's the part i don't understand

am i suppose to use equal the formulas?

YEs, equate the formulas to the numbers you were given.

If I remember correctly, you were given momentum, and KEnergy.

mv= somenumberA
1/2 mv^2= somenumberB.

divide the second equation by the first to get..

1/2 v= somenumberB/somenumberA
that will give you velocity, then substitute back in to get mass.

Frankly, I don't remember the problem well enough to get to specifics.

still don't get it

COULD YOU EXPLAIN this to me

see above.