Answer: x = 27
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Step-by-step explanation:
Complementary angles always add to 90 degrees. Think of the "co" in "complementary" matching with the "co" in "corner" to help remember this. This is in contrast to supplementary angles which form a straight 180 degree angle (both "supplementary" and "straight" start with "s")
Because the 40 and 2x-4 angles are complementary, they add to 90 and we can solve for x like so:
40+(2x-4) = 90
2x+36 = 90
2x = 90-36 .... subtracting 36 from both sides
2x = 54
x = 52/2 .... divide both sides by 2
x = 27