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**Hint:**Sum of the interior angles of a triangle is 180˚.

Concave quadrilaterals are the quadrilaterals which have at least one interior angle greater than 1800.

**Complete step-by-step answer:**(i) Since, the sum of the three angles of a triangle is 180˚, we can say that in Δ ABC:

∠ A + ∠ B + ∠ C = 180˚

On putting values of angle A and angle C,

⇒ 40˚ + ∠ B + 90˚ = 180˚

On simplifying,

⇒ ∠ B = 180˚ - 40˚ - 90˚ = 50˚

Now, in Δ BDE:

∠ B + ∠ D + ∠ E = 180˚

On putting values,

⇒ 50˚ + x˚ + 100˚ = 180˚

⇒ x˚ = 180˚ - 50˚ - 100˚ = 30˚

(ii) By giving a part of his land for a health care center for the villagers, Ram depicts the qualities of generosity, responsibility, optimism etc.

**Note:**In general, the sum of the exterior angles of any polygon is always 360˚.

Since, there are n angles in an n-sided polygon and the sum of an interior angle and its exterior angle is 180˚, we may calculate that the sum of the interior angles will be (180n - 360)˚.

For a triangle, the sum of the interior angles is always: 180 × 3 - 360 = 540 - 360 = 180˚.

For a quadrilateral, the sum of the internal angles is always: 180 × 4 - 360 = 720 - 360 = 360˚.

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