If the mass of 4.52xx"10"^(-3) "mol C"_20"H"_42"4.52×10−3mol C20H42 is what you are looking for:
Determine the molar mass of "C"_20"H"_42"C20H42.
"Molar mass"Molar masscolor(white)(.). "C"_20"H"_42: C20H42:(20xx"12.0 g/mol C")+(42xx"1.0 g/mol H")="282 g/mol C"_20"H"_42"(20×12.0 g/mol C)+(42×1.0 g/mol H)=282 g/mol C20H42
Mass of 4.52xx"10"^(-3) "mol C"_20"H"_42"4.52×10−3mol C20H42
Multiply mol "C"_20"H"_42"C20H42 by its molar mass.
4.52xx"10"^(-3) color(red)cancel(color(black)("mol C"_20"H"_42))xx(282"g C"_20"H"_42)/(1color(red)cancel(color(black)("mol C"_20"H"_42)))="1.27 g C"_20"H"_42" rounded to three significant figures