5 toppings because
1.5*5= 7.5 7.5+10=17.5
and
1*5=5 5+12.5= 17.5
pizza a=1.5x+10
pizza b=1x+12.50
1.5x+10=1x+12.50
.5x+10=12.5
.5x=2.5
2.5/.5= 5
