a+a(3/4)=21

Solution for a+a(3/4)=21 equation:

a+a(3/4)=21

We move all terms to the left:

a+a(3/4)-(21)=0

We add all the numbers together, and all the variables

a+a(+3/4)-21=0

We multiply parentheses

3a^2+a-21=0

a = 3; b = 1; c = -21;
Δ = b2-4ac
Δ = 12-4·3·(-21)
Δ = 253
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-\sqrt{253}}{2*3}=\frac{-1-\sqrt{253}}{6}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{253}}{2*3}=\frac{-1+\sqrt{253}}{6}
$