Answer:
20
Step-by-step explanation:
The <C in the triangle and 100 make a straight line so they add to 180
<C + 100 = 180
<C = 80
<B = <C since this is an isosceles triangle and they are the base angles
<A + <B + <C = 180 since the angles of a triangle add to 180
<A + 80 + 80 = 180
Combine like terms
<A +160 = 180
Subtract 160 from each side
<A +160-160 = 180-160
<A =20
