I)a + 15%a = 3500 lei
a+ 15a/100 =3500
²⁰⁾a+3a/20 = ²⁰⁾3500
20a + 3a = 70000
23a = 70000 => a = 70000:23 => a=3043,48 lei
3043,48+ (15/100) x3043,48 = 3043,48 + 456,52 = 3500
II) b₁ = b -10%b = ¹⁰⁾b-b/10 = 9b/10
b₂ = b₁-10%b₁ = 70 lei
b₂ = ¹⁰⁾9b/10 - (9b/100) = (90b-9b)/100 = 81b/100
81b/100 =70 => b = 70x100:81 = > b = 86,42 lei
III) in poza