Thanks in advance!
The 55o angle cuts off two arcs: the larger arc is 100o + 35o = 135o.
The smaller arc is xo.
So: angle(G) = [ arc(BCD) - arc(EF) ] / 2
55o = [ 135o - x ] / 2
110o = 135o - x
-25o = -x
x = 25o