Answer:
x=-11
What we know=
Angles A'=x+51
Angle B=60
Angle C=80
Angle B' and C'=?
Due to the vertically opposite angle rule, we know angle B' and C' are the same as angle B and C.
So, angle B' is 60 degrees. Angle C' is 80 degrees.
We can add them together to get 140 degrees.
So we have 140, x+51. We can make an equation.
We can combine like terms (140 and 51) to get 191
A triangle only adds up to 180 degrees. So now you can subtract 180-191=to get x.