Answer:
61
Explanation:
first we set <B and <E equal to each other to find x (they are equal because it is a given in the phrase below the pics)
5x + 8 = 7x - 12
5x + 20 = 7x
20 = 2x
10 = x
now we know x is 10, so substitute it into an equation to find the measure of the vertex of the triangles
5(10) + 8 = 58
subtract 58 from 180 to find what the base angles are combined
180 - 58 = 122
since there are two congruent base angles (the base angles of isosceles triangles are always congruent), we have to divide 122 by 2 to find the measure of a base angle
122 ÷ 2 = 61
<F is a base angle, so <F is 61