[(6×a+90×5):9+36]:2=68

[ ( 6 x a + 90 x 5 ) : 9 + 36 ] : 2 = 68

( 6 x a + 450 ) : 9 + 36 = 68 x 2 = 136

( 6 x a + 450 ) : 9 = 136 - 36 = 100

6 x a + 450 = 100 x 9 = 900

6 x a = 900 - 450 = 450

a = 450 : 6

a = 75 → numarul necunoscut, aflat prin metoda mersului invers

[(6×a+90×5):9+36]:2=68

(6×a+90×5):9+36 = 136

(6×a+90×5):9 = 100

6×a+450 = 900

6a = 450

a= 75

Sper ca te-am ajutat ! Seara frumoasa ! (;