If 32.0 g of mgso4⋅7h2o is thoroughly heated, what mass of anhydrous magnesium sulfate will remain?

Find moles of MgSO4.7H2O

molar mass = 246
so moles  = 32 / 246  = 0.13 moles.

When heated, all 7 H2O from 1 molecule will be gone. 
total moles of H2O present = 7 x 0.13 = 0.91
mass of those H2O = 0.91 x 18  = 16.38g

so mass of anyhydrous MgSO4 remain = 32 - 16.38 = 15.62 g

Answer charle's law