Answer:
a = -12
Step-by-step explanation:
For two lines to meet at a right angle, they are perpendicular to each other. Therefore the product of the slopes of the two lines is -1.
The slope of 3y + x = 0 will be -1/3 (rearrange the terms, 3y = -x and therefore y = -1/3 x).
The slope of 4y + ax + 3 = 0 will be -a/4. (4y = -ax - 3, therefore y = -a/4 x - 3/4)
Since the product of the slopes is -1, we can set up an equation now.
-1/3 * -a/4 = -1
a/12 = -1
a = -12
