[2×(2×a+2×2)+4]÷15=4

Sper  sa  te  ajute. succes

[ 2 × ( 2 × a + 2 × 2 ) + 4 ] : 15 = 4

2 × ( 2 × a + 4 ) + 4 = 4 × 15

2 × ( 2 × a + 4 ) + 4 = 60

2 × ( 2 × a + 4 ) = 60 - 4

2 × ( 2 × a + 4 ) = 56

2 × a + 4 = 56 : 2

2 × a + 4 = 28

2 × a = 28 - 4

2 × a = 24

a = 24 : 2

a = 12 → numarul, aflat prin metoda mersului invers