Just take both sides multiply by 2 then divide 3
Answer:
(a)Therefore the value of x=
(b) Therefore the value of x 
Step-by-step explanation:
Horizontal tangent line: The first order derivative of a function gives the slope of the tangent of the function. The slope of horizontal line is zero.If the slope of tangent line is zero then the tangent line is called horizontal tangent line.
(a)
Given function is,

Differential with respect to x

For horizontal tangent line, f'(x)=0
3+ 3 cos x= 0
⇒3 cos x=-3
⇒cos x=-1
⇒x = 180° 
Therefore the value of x=
(b)
Given that, the slope is 3.
Then,f'(x)=3
3+ 3 cos x= 3
⇒3 cos x= 3-3
⇒cos x=0
⇒x = 90° 
Therefore the value of x 
The correct answer would be 16/24. You would need to multiply both the denominator and numerator by 4.
if you can plz rewrite this that way i can help