We are given that the cost of each shirt = $12.25
It is given that she bought total 'x' shirts, each of cost $12,25.
So, the cost of 'x' shirts is dollars
Also, there is a shipping charge of $3.99
So, the total cost of 'x' shirts is
Since, the shirts cost her total $77.49.
We have the equation,
12.25x + 3.99 = 77.49