Let $x$ be the original price. Express the sale price (which is $68$) as a percentage of $x$ and write an equation like "(percent as a decimal)$\times x = 68$".

After you have an equation, isolate $x$ by dividing. Be careful to divide by the correct decimal that represents the remaining percentage.

Take your result and calculate 15% of it, then subtract that from the original. Do you get $68$ back?

In a new expression line, type 68/0.85 (since the sale price is 85% of the original). Look at the numeric result that Desmos gives; that value is the original price before the 15% discount.

A 15% discount means the customer pays 100% − 15% = 85% of the original price.

Let $x$ be the original price. Then the sale price is $85\%$ of $x$, which we can write as:

So we need to solve this equation for $x$.

To isolate $x$, divide both sides of the equation by $0.85$:

Now compute this fraction.

Compute $\frac{68}{0.85}$.

One way is to rewrite it without decimals:

• Multiply numerator and denominator by 100:

• Now divide: $6800 \div 85 = 80$.

So the original price $x$ is $80$ dollars, which corresponds to choice C.