hey there !
a) Pb(SO4)2 => lead(II) sulfate
b) The molar mass of this compound was calculated from the amount of atoms of each element, with its respective atomic masses
Pb = 207.2 a.m.u
S = 32.065 a.m.u
O = 15.9994 a.m.u
Therefore:
Pb(SO4)2 = 207.2 + 32.065 * 2 + 15.9994 * 8 => 399.3252 g/mol
hope this helps!