How do u know that your answer is incorrect i attempted your problem your equation m1v1+m2v2=(m1+m2)vf appears correct to me it gives 550*7.2+0=(550+m2)4.7 and I got an answer of 292.55 kg.
Multiple Pulleys and determing Tension Dynamics
So i started out with the the equation for the tension of the block-pulley system on the far left in the y direction being: 2T-2g = 2*a1
the equation for the middle block-pulley system is: 2T-2g = 3*a2
the equation for the block on the ramp is...