First you find the RFM (Relative Formula Mass) of Fe2O3
Fe2 = 56 x 2
= 112
O3 = 16 x 3
= 48
112 + 48 = 160
Moles = mass/RFM
= 79.2/160
=0.495
Then you rearrange the formula
Mass= moles x RFM
= 0.495 x 112
= 55.44 g
(To find mass of Iron have to use RFM of total iron in the substance example Fe2 ^^)
