Let $x be the price before sale. This price is 100%. If in a sale, Jen buys a laptop for $351.55 that is 21% less than the price before the sale, then this price is 100%-21%=79%.
Consider proportion
$x - 100%,
$351.55 - 79%,
that is mathematically
[tex]\dfrac{x}{351.55}=\dfrac{100}{79}.[/tex]
Find x:
[tex]x=\dfrac{351.55\cdot 100}{79}=445.[/tex]
Answer: the price before the sale was $445.
