3=7x-x^2

Solution for 3=7x-x^2 equation:

3=7x-x^2

We move all terms to the left:

3-(7x-x^2)=0

We get rid of parentheses

x^2-7x+3=0

a = 1; b = -7; c = +3;
Δ = b2-4ac
Δ = -72-4·1·3
Δ = 37
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-\sqrt{37}}{2*1}=\frac{7-\sqrt{37}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+\sqrt{37}}{2*1}=\frac{7+\sqrt{37}}{2}
$