31=3(y+7)5y

Solution for 31=3(y+7)5y equation:

31=3(y+7)5y

We move all terms to the left:

31-(3(y+7)5y)=0


We calculate terms in parentheses: -(3(y+7)5y), so:

3(y+7)5y

We multiply parentheses

15y^2+105y

Back to the equation:

-(15y^2+105y)


We get rid of parentheses

-15y^2-105y+31=0

a = -15; b = -105; c = +31;
Δ = b2-4ac
Δ = -1052-4·(-15)·31
Δ = 12885
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-105)-\sqrt{12885}}{2*-15}=\frac{105-\sqrt{12885}}{-30}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-105)+\sqrt{12885}}{2*-15}=\frac{105+\sqrt{12885}}{-30}
$