Question

3x+30=5x+40 my answer was - 5. Is it right.

Answer 1

3x+30=5x+40
3x-5x=40-30
-2x=10
x=10/-2
x=-5
So,your ans. is right

Answer 2

To verify or check the answer, substitute your answer in X value. If LHS = RHS then your answer is correct.

Let us see,

3x + 30 = 5x + 40
3 ( -5 ) + 30 = 5 ( -5) +40
-15 +30 = -25 +40
15 = 15.
LHS =RHS
your answer is correct.

I hope you like it
tq