Can someone please help me with the following question

:

Paul has twenty-five transit cards, each worth either$5, $3, or $1.50. What

is the total monetary value of all of Paul's transit cards?

Answer:

values of cards: 5x + 3y + 1.50(25 - x - y) = ?

Simplify ~ 3.5x + 1.5y + 37.5 = ?

From here I tried solving for x and y.. Here's what I did, please do correct me if I'm wrong (most probably am

)

y = (-37,5 - 3,5x)/1,5

so, 3,5x + 1,5(-37,5 - 3,5x)/1,5 + 37,5 =

3,5x + -37,5 - 3,5x + 37,5 = x = 0

And then I got stuck