<1 + <2 + <3 = 360
given <1 = 90
so
90 + x - 7 + 2x = 360
3x + 83 = 360
3x = 277
x = 277/3
m<3 = 2(277/3)
m<3 = 554/3
m<3 = 184.67 degrees.
