In this problem you would set these two equations equal to each other.
$8+ $1.50x = $10+ $1x
After this you would simplify the equation to isolate x (being the number of toppings you put on the pizzas)
$8+ 1.50x =$10+ 1x
-8 -8
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$1.50x = $2 + $1x
-1x -1x
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$.50x/.50 = $2/.50
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x= 4 toppings and the pizzas would equal $14 total