How do you calculate molar mass? For example, what is the molar mass of Cu(NH_4)_4SO_4?

$\text{Molecular mass of } C u S {O}_{4} \cdot {\left(N {H}_{4}\right)}_{4}$ $=$
$\left(63.55 + 32.06 + 4 \times 16.00 + 4 \times 14.01 + 16 \times 1.00794\right) \cdot g \cdot m o {l}^{-} 1 \cong 250 \cdot g \cdot m o {l}^{-} 1$