Answer:
m<A=117°
Explanation:
Based on the given from the problem, we know that angle A and angle B are vertical angles
Vertical angles are congruent; they have the same value.
we know that the measure of angle A is (5x-3)° and the measure of angle B is (4x+21)°
since we know they are congruent via vertical angles theorem, we can make the two values equal to each other
5x-3=4x+21
add 3 to both sides
5x=4x+24
subtract 4x from both sides
x=24
we found the value of x. However, the question asks for the value of angle A, which is (5x-3)°
we substitute our known value to find the value of angle A
m<A= (5*24-3)°
m<A=(120-3)°
m<A=117°
the measure of angle A is 117°
Hope this helps!