#### Explanation:

The formula for calculating salary is:

$S = p + r \cdot c$ where $S$ is the total salary, $p$ is the base pay, $r$ is the commission rate and $c$ is the number of units the commission is applied to.

However because question states "to have over $250$i t i s a n \in e q u a l i t y \mathmr{and} i t i s a \text{greater than} \mathmr{and}$># inequality because it does not say "to have$250 or more". We can write this inequality as:

$p + r \cdot c > S$

We know the total salary we are shooting for, we know the base pay and we know the commission rate. We can substitute these into the equality and solve the inequality for $c$ while keeping the equation balanced:

$50 + 3 \cdot c > 250$

$50 + 3 \cdot c - 50 > 250 - 50$

$3 \cdot c > 200$

$\frac{3 \cdot c}{3} > \frac{200}{3}$

$c > 66.7$

Assuming sales are in whole units or integer units then to make more than $250 the solution should be rounded up to the next whole number - $67\$