Here we have to use the theorem tht exterior angle is the sum of non adjacent interior angles. That is ,
z = x+y
And the values of x,y and z are given in terms of n. On substituting these values for x,y and z, we will get
151-5n = 4n-18+n+9
Combining like terms of the right side
151-5n = 5n -9
Moving 5n to the right side and 9 to the left side,
151+9 = 5n+5n
160=10n
Dividing both sides by 10
n = 16
Now we need to find the value of z when n =16. SO we substitute the value of n in z, that is
z =151-5(16) =151-80 = 71 degree .
So the correct option is A
