Lines are perpendicular if the slope of one is the negative reciprocal of the other. In this case the slopes are -8/3 and 8/3, so while negative they are not reciprocal. So no, the two lines intersect but are not perpendicular.
third option is the correct answer....
The expression can be simplified as:
k^3(k7/5)^-5
= k^(3+-5) * (7/5)^-5
(Collecting the powers of k at one side and the constants at other side)
= k^-2 * (5/7)^5
(Solving thr integer powers)
= k^-2 * (3125/16807)
