Let n be the number of sides:
Sum of all interior angles of a polygon = (n – 2) 180o
Four angles measure 100o each and remaining angles (i.e n – 4) measure 160o each
100(4+(n-4) *160 = (n-2)180
400+160n-640 = 180n – 360
760-640 = 20n
n = 6
Hence the number of sides of the polygon = 5=6