From the given information, the measure of DEF is 81°
From the question, we are to determine the measure of DEF
From the given information,
DEF and RST are complementary angles. This means they sum up to 90°
Thus,
(3(-5 + 2x)) + (x - 7) = 90
(3(-5 + 2x)) + (x - 7) = 90
(-15 + 6x) + (x - 7 ) = 90
-15 + 6x + x - 7 = 90
6x + x = 90 + 15 + 7
7x = 112
x = 112/7
x = 16
Then, substitute the value of x to determine the measure of DEF
(3(-5 + 2x))
= (3(-5 + 2(16)))
= (3(-5 + 32))
= (3(27))
= 81°
Hence, the measure of DEF is 81°
Learn more on Calculating the measure of angles here: https://brainly.com/question/12047360
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