Cheese pizzas are 2/3 of the pizza's purchased because 2 / (2+1) = 2/3
She buys 4 cheese pizzas because 6 x (2/3) = <<6*2/3=4>>4
These give her 72 pieces of cheese pizza because 4 x 18 = <<4*18=72>>72
The students at 64 pieces of cheese because 72 - 8 = <<72-8=64>>64
There are 32 students in her class because 64 / 2 = <<64/2=32>>32
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