ABC congruent DEF find the measure of the given angles or the lengths of the given sides

m∠B = 21°

Step-by-step explanation:

Congruent triangles have equal angles, equal sides, equal perimeters, and equal areas

Let us solve the question

∵ The two triangles ABC and DEF are congruent

∴ m∠B = m∠E

∵ m∠B = 3y

∵ m∠E = 21

→ Equate their measures

∴ 3y = 21

→ Divide both sides by 3

∵ =

∴ y = 7

→ Substitute y by 7 in the measures of angle B to find it

∵ m∠B = 3(7)

∴ m∠B = 21°