I must also show my work, but I do not know how to do this problem

Answer:
x = 10
Step-by-step explanation:
We know that the sum of angles in a triangle is equal to 180 degrees;
This means that
71+50+(6x-1) = 180; now that you have an algebraic expression, you can solve for x.
71+49+6x=180
120+6x = 180
6x = 60
x = 10