Answer
$\frac{20t+8}{(3t+1)^{3/2}}$
Work Step by Step
Start with cancelling the common factor $(3t+1)^{-3/4}$, we have:
$\frac{7(3t+1)^{1/4}-(t-1)(3t+1)^{-3/4}}{(3t+1)^{3/4}}=\frac{7(3t+1)^{1/4+3/4}-(t-1)}{(3t+1)^{3/4+3/4}}=\frac{7(3t+1)-(t-1)}{(3t+1)^{3/2}}=\frac{20t+8}{(3t+1)^{3/2}}$