Răspuns :
[(2*a+178)*15+90]=630*45
[(2*a+178)*15+90]=28,350
[(2*a+178)*15]=28,350-90
[(2*a+178)*15]=28,260
(2*a+178)=28,260:15
(2*a+178)=1,884
2*a=1,884-178
2*a=1,706
a=1,706:2
a=853
[(2*a+178)*15+90]=28,350
[(2*a+178)*15]=28,350-90
[(2*a+178)*15]=28,260
(2*a+178)=28,260:15
(2*a+178)=1,884
2*a=1,884-178
2*a=1,706
a=1,706:2
a=853
[( 2 x a + 178 ) x 15 + 90 ] : 45 = 630
( 2 x a + 178 ) x 15 + 90 = 630 x 45
( 2 x a + 178 ) x 15 + 90 = 28 350
( 2 x a + 178 ) x 15 = 28 350 - 90
2 x a + 178 = 28 260 : 15
2 x a + 178 = 1 884
2 x a = 1 884 - 178
2 x a = 1 706
a = 1 706 : 2
a = 853 numarul, aflat prin metoda mersului invers
( 2 x a + 178 ) x 15 + 90 = 630 x 45
( 2 x a + 178 ) x 15 + 90 = 28 350
( 2 x a + 178 ) x 15 = 28 350 - 90
2 x a + 178 = 28 260 : 15
2 x a + 178 = 1 884
2 x a = 1 884 - 178
2 x a = 1 706
a = 1 706 : 2
a = 853 numarul, aflat prin metoda mersului invers