The slope of the line
is
.
The line perpendicular to the above line has slope
Its equation is
. Since this line passes through,
,

Thus the equation of the line in slope intercept form is 
The answer is all real numbers for x
because simplifying, you get both sides are equal
Do you have a picture or something to accompany the question?
First you need to combine like terms
7-3x= 5x+13
step 1 add 3x
7=8x+13
step 2 subteact 13
-6=8x
step 3 divide both sides by two
x=-3/4