Notam x=suma pe care o avea
A donat 15% si i-au ramas 1020 lei , adica x-15%x=1020
[tex]x-\frac{15}{100}\times x=1020\\\\ \frac{85x}{100}=1020\\\\ x=\frac{1020\times 100}{85} =1200\ lei[/tex]
x=1200 lei
Maria a donat 180 lei
[tex]\frac{15}{100}\times 1200= 180\ lei[/tex]