A straight line adds up to 180
So the line opposite of 137 should add up to 180
This gives us the equation 137+x=180 then x=43
The triangle also adds up to 180 degrees
So 102+43+x=180
The equation can be simplified to 145+x=180 therefore x=35
So x+?=180 because it is a straight line.
We can substitute x in making the equation 35+?=180
Now we want to solve for the ? so we'll subtract 35 from each side
This leaves us with the equation ?=145
So we now know that the ?=145