Answer:
D. 6
Explanation:
Mark watches 16 movies per month and has been for x months; this gives us the expression 16x.
Max watches half as many as Mark has; this means we multiply Mark's expression, 16x, by 1/2:
1/2(16x)
Together they have watched 144 movies. This gives us the equation
16x+1/2(16x) = 144
Simplifying the second term, we have
16x+8x = 144
Combining like terms gives us
24x = 144
Divide both sides by 24:
24x/24 = 144/24
x = 6