Răspuns:
x = 9
Explicație pas cu pas:
3·{10+2·[40-2·(28-3·5)]}-7x = 51 <=>
3·{10+2·[40-2·(28-15)]}-7x = 51 <=>
3·{10+2·[40-2·13]}-7x = 51 <=>
3·{10+2·[40-26]}-7x = 51 <=>
3·{10+2·14}-7x = 51 <=>
3·{10+28}-7x = 51 <=>
3·38-7x = 51 =>
114 - 51 = 7x =>
63 = 7x =>
x = 63:7 =>
x = 9
