Question

n/2 - 3n/4 + 5n/6=21

Answer 1

hope my answer would help you

Answer 2

$LHS = \frac{n}{2} - \frac{3n}{4} + \frac{5n}{6} \\ = \frac{2n - 3n}{4} + \frac{5n}{6} \\ = \frac{5n}{6} - \frac{n}{4} \\ = \frac{10n}{12} - \frac{3n}{12} \\ = \frac{7n}{12} \\ RHS = 21 \\ n= (12*21)/7 \\ n =36$

For a nincompoop like the questioner, here's the dummy version:

n/2-3n/4+5n/6=21

>> (2n-3n)/4 + 5n/6=21

>> -n/4 + 5n/6= 21

>> (-3n+10n)/12=21

>> 7n/12=21

>> n= (21×12)/7

>>n=12×3

>> n=36