1.5(5) + 12/3 + 3x = 22
7.5 + 4 + 3x = 22
11.5 + 3x = 22
3x = 22 - 11.5
3x = 10.5
x = 10.5/3
x = 3.5....so they cost 3.50 per kg
1/1000 = x/100...1 kg to 1000 g = x kg to 100 g
cross multiply
1000x = 100
x = 100/1000
x = 1/10...so 100 grams = 1/10 of a kg
so 1/10 * 3.50 = 3.50/10 = 0.35 <== cost of 100 grams