Answers:
angle FHG = 42 degrees
angle GHI = 100 degrees
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Step-by-step explanation:
FHI is the largest angle. It is split into two pieces FHG and GHI which have measures of (3x+6) and (9x-8) degrees respectively.
Put another way, those two smaller angles (FHG and GHI) combine to form the larger angle (FHI)
This is the angle addition postulate.
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(angle FHG) + (angle GHI) = angle FHI
(3x+6) + (9x-8) = 142
3x+6+9x-8 = 142
(3x+9x) + (6-8) = 142
12x - 2 = 142
12x-2+2 = 142+2 ... adding 2 to both sides
12x = 144
12x/12 = 144/12 .... dividing both sides by 12
x = 12
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Use that x value to find the angles we're after
angle FHG = 3x+6 = 3*12+6 = 36+6 = 42
angle GHI = 9x-8 = 9*12-8 = 108-8 = 100
Note how
(angle FHG) + (angle GHI) = 42 + 100 = 142
which is the measure of angle FHI. This confirms the answers.