The leftmost triangle has two angles labeled 40° and 70°. Subtract these from 180° (the sum of the angles in any triangle) to determine that the third angle is 70°. Subtract 130 – 70 = 60° to get the measure of the adjoining angle in the rightmost triangle. Since the leftmost triangle is isosceles, the two long sides are each equal to 10. Since the rightmost triangle is a 30–60–90 triangle, the sides are in the proportion \(x: \sqrt{3} x : 2x\)

Because the hypotenuse is 8 and also the 2x in the ratio, the shortest leg of this triangle is x = 4. To calculate x, subtract: 10 – 4 = 6. The two quantities are equal.