8 units
(This is how I get the answer)
Given that,
Point = (-5,3)
Slope, m = -3/5
To find,
The slope intercept form of the equation of the line.
Solution,
The general form of equation is :
y = mx +b
We have, x = -5, y = 3
So,

The equation is :

Hence, the required equation is
.
The answer is 16 units
An easy way to find the perimeter is remembering the formula of a+b+c.
So in this case, you count how many units each line of the triangle it covers. 4+6+6= 16