This pentagon can be split into three triangles, so the total for this pentagon is 540°. Add up all angles to equal 540°.
x= unknown angle
90° + 107° + 144° + 138° + x= 540°
479 + x= 540
subtract 479 from both sides
x= 61
CHECK:
90 + 107 + 144 + 138 + 61= 540
540= 540
ANSWER: x= 61°
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