Use (n - 2) × 180 to find the sum of the measures of the interior angles of the polygon, where n = number of sides of the polygon.
The polygon has 7 sides, so plug 7 in for n.
(7 - 2) × 180 = 900
The sum of the interior angles of this 7-gon is 900°.
Now that we know this, make an equation where all the interior angles add up to 900, then solve for x.
∠A + ∠B + ∠C + ∠D + ∠E + ∠F + ∠G = 900° ⇒
146 + 122 + 142 + 140 + 110 + 142 + x = 900
802 + x = 900
Subtract 802 from both sides.
x = 98°