Answer:

Step-by-step explanation:
we have
Line 1

Equation in slope intercept form
The slope is equal to

Line 2


Equation in slope intercept form
The slope is equal to

we know that
If two lines are perpendicular, then their slopes are opposite reciprocal (the product of the slopes is equal to -1)
so

substitute


I believe that the answer is 120 marbles.<span />