Answer
The original price of the dress was $120$ dollars
Work Step by Step
$y=x-0.15x$->$y=0.85x$
x is the original price
y is the sales price
The sales price is equal to the original price minus 15% of the original price
$91.80=y-0.1y$->$91.8=0.9y$
91.80 = sales price - 10%
$91.80-0.9(0.85x)$
$91.8=0.765x$
$\frac{91.8}{0.765}=\frac{0.765}{0.765}x$
$120=x$
