The of tin in the compound will be equal to the ratio between the mass of tin and the mass of the compound, multiplied by
$color(blue)("% Sn" = m_(Sn)/m_"total" xx 100)$
Your initial sample of tine reacts completely with
$m_"total" = "20.50 g" + "24.49 g" = "44.99 g"$
The of tin in the compound will be
$(20.50 color(red)(cancel(color(black)("g"))))/(44.99color(red)(cancel(color(black)("g")))) xx 100 = color(green)("45.57% Sn")$
Now, to get the compound's , use the molar masses of the two to determine how many moles of each you have in that sample
$20.50 color(red)(cancel(color(black)("g"))) * "1 mole Sn"/(118.71color(red)(cancel(color(black)("g")))) = "0.17269 moles Sn"$
$24.49 color(red)(cancel(color(black)("g"))) * "1 mole Cl"/(35.453 color(red)(cancel(color(black)("g")))) = "0.69077 moles Cl"$
Divide both values by the smallest one to get the that exists between the two elements in the compound
$"For Sn: " (0.17269 color(red)(cancel(color(black)("moles"))))/(0.17269 color(red)(cancel(color(black)("moles")))) = 1$
$"For Cl: " (0.69077 color(red)(cancel(color(black)("moles"))))/(0.17269color(red)(cancel(color(black)("moles")))) ~~ 4$
The empirical formula of the compound, which tells you the smallest whole number ratio that exists between the two elements, will be
$"Sn"_1"Cl"_4 implies color(green)("SnCl"_4)$