No, that formula is no good for calculating mass.
I would go about it this way.
moles needed = M x L = 0.442 x 0.800 = ??
Then moles = grams/molar mass. You know moles from the first calculation and you know molar mass, solve for grams.
What mass of MgSO4 · 7H2O is required to prepare 800 mL of a 0.442MMgSO4 solution?
Answer in units of g.
Would you use the formula M1V1=M2V2?
2 answers
What is the molar mass?