This is more algebra than geometry. You know the 3 angles in a triangle add up to 180º. It turns out the 4 angles in a 4 sided figure add up to 360º. Juanita gave you the formula for a polygon with n sides, which is nice to know.
for your problem, write down the sum of the angles and set equal to 360
94+86+94+11x-2= 360
btw, we see that angle F=86 + angle G=94 add up to 180 degrees
that means the top and bottom edges are parallel.
also, angles F=86 and E=94 add up to 180, so the 2 side edges are parallel
you have a parallelogram, so you know the angles in opposite corners are equal.
so you could write
11x-2= 86
but the first equation simplifies to this one, so you don't need to know you have a parallelogram
now do algebra to find x. First add +2 to both sides
11x -2 + 2= 86+2
simplify, using -2+2=0 and 11x+0 is just 11x (on the left side). the right side is 88
11x= 88
divide both sides by 11
11x/11 = 88/11
you get
x=8