Part A :
100% + 20% = 120% = 1,2
1,50 : 1,2 = $1,25 - the price in september.
Part B :
1,25 * 900 = $1125 - they sold in september
40% = 0,4
1125 * 0,4 = $450 - they earned in september
1,50 * 700 = $1050 - they sold in october
1050 * 0,4 = $420 - they earned in october
450 > 420
The seventh-grade class earned more money in september.