a)
M_C_O_2 = 12g + 16g*2 = 12g + 32g = 44g
44g - 1 mol
20g - x
x = \frac{1mol * 20g}{44g} \approx 0.45 mola
b)
M_S = 32g
32g - 1 mol
14g - x
x = \frac{14g*1mol}{32g}=0.4375 mola
c)
M_A_g = 108g
108g - 1 mol
0.03g - x
x = \frac{1mol*0.03g}{108g} \approx 0.00028 mola