Let J be the jacket and S the shirts. Jade wants to know how many shirts she can buy.
Then, we can write the following relationship:

since Jade only wants one jacket, this means that J=1. Then, by substituting these value into our formula, we have

which gives

Now, if we move 25 to the right hand side as -25, we obtain

and finally, we have

that is, Jade can buy 5 shirts and 1 jacket with $80.