What is the m∠acb? 10° 50° 90° 180°

The total sum of angles in a triangle is 180, thus the value of ∠ACB will be obtained as follows:
Given that the triangle is a right triangle, the sum of angles will be:
(4x)°+(7x-20)°+90=180
simplifying and solving for x we get:
4x+7x-20+90=180
11x=180+20-90
11x=110
dividing both sides by 11 we get:
(11x)/11=110/11
this gives us
x=10°
Thus substituting the value of x in:
∠ACB=(7x-20)° 
=(7*10-20)
=70-20
=50°

50°