so quick check that your values are correct
maria=360 times 0.75=270 check
debbie=maria-60=270-60=210
so the discount total is
total origonal cost-total paid=360-210=150
discount =150
to convert to percent make fraction
150/360=discount simplify=15/36=5/12=0.41666
percent means parts out of 100 so
0.416666=0.41666/1
multiply top and bottom by 100 or multipy whole by 100/100
0.41666/1 times 100/100=41.666/100=41.67% rounded
she got 41.67% discount