3t+u=561

7b+t=906

2b+7t+5u=1758

what are t, u, and b

(give me the numbers)

Show your work

Look, solve it first for" b "

u=561 - 3t

t = 906 - 7b

So, 2b+7 (906 - 7b) + 5 (561 - 3 (906-7b) = 1758

gain the b then substitute by the result in the second equation then gain the value of t and solve the first equation.