how would ypu prepare 80.00mL of a 7.5% solution of MgSO4 7H2O using solid MgSO4 7H2O and water?

Answer 1

7.5 percent w/v?

.075(80)= 6 grams MgSO4 = 6/120=.05 moles
but moles of the hydrated salt will have a mass of .05*246.5=12.32 grams.

So add 12.32 grams of the salt, and add water while stirring to the 80ml mark.

Now if the .075 is w/w, it is a different issue.