Answer
$y=2x+1$
Work Step by Step
Lets assume that Equation for tangent line is :
$y=ax+b$
İf this line is tangent to any $f(x)$ at $(x,y)$ point then
$f’(x)=a$
İn this problem $f\left( x\right) =4x-x^{2}$ and coordinate is $(1,3)$ so
$a=f'\left( 4x-x^{2}\right) =4-2x\Rightarrow f'\left( 1\right) =2=a$
$y=a\times x+b\Rightarrow b=y-a\times x=3-2\times 1=1$
So the equation is
$y=2x+1$
