(v+3)³+56=0 simplify

Subtract 56 from both sides

(v +3)^3 = -56    take the cubed root of both sides

v + 3  = (-56)^(1/3) = -(56)^(1/3)  = -(8*7)^(1/3) = -2(7)^(1/3)   subtract 3 from both sides

v =    -3 -2(7)^(1/3)=  -(3+ 2³√7)