I broke it all the way day half of 51 is 25 in a half and half of 25 is 12 in half so if Jimmy lifted twice as much he may have lifted 25 in a half and bob left 12
A, B and E.
Adding and multiplying the terms allow them to keep working. However, you must make sure that each variable is changed each time. Not just one as in C and D.
It is 24. 6 x 4= 24.
Hoped this helped.
~Bob Ross®