B.) 45°

C.) 54°

D.) 60°

E.) 72°

**The angles of a triangle add up to 180°.**

Therefore, the angles of two triangles add up to 360°.

Therefore, the angles of two triangles add up to 360°.

**The only known angle is 90°.**

The unknown angles add up to 270°.{subtracted the known angle, 90°, from the sum of all the angles, 360°}

The unknown angles add up to 270°.

a + b + c + d + e = 270

a + b + c + d + e

---------------- = average of the five angles {added numbers and divided by the number of numbers}

5

270

----- = average of the five angles {substituted 270 for the sum of the unknown angles}

5

54 = average {divided}

**C.) 54°**

**Ask Algebra House**