Answer: B) 21
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Explanation:
The base angles are congruent in this isosceles trapezoid, so 7x and 4x+9 are equal to each other
Let's solve for x
7x = 4x+9
7x-4x = 4x+9-4x .... subtract 4x from both sides
3x = 9
3x/3 = 9/3 ..... divide both sides by 3
x = 3
If x were equal to 3, then
base angle = 7*x = 7*3 = 21
or
base angle = 4*x+9 = 4*3+9 = 12+9 = 21
Both base angles are 21 degrees each
