Answer
We wrote $18$ checks this month.
Work Step by Step
First, we need to set up an equation that we can solve.
The unknown in this case is the number of checks we can write if we are charged a total of $6.90$. Let us use $x$ to denote this unknown. We will multiply $x$ by $0.05$ to get how much we will be charged for the amount of miles we drive.
The bank will charge us $6$ dollars, regardless of how many checks we write, so $6$ is a constant.
To be able to calculate the total charges, we will add $6$ to $0.05x$. We want this amount to equal $6.90$ because that is the amount we had been charged by the bank.
The equation we get is:
$$0.05x + 6 = 6.90$$
We subtract $6$ from each side of the equation to isolate the variable to one side of the equation:
$$0.05x = 0.90$$
We divide both sides by $0.05$ to solve for $x$:
$$x = 18$$
We wrote $18$ checks this month.
