An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite:

d° = b° + c°

To find angle c, remember that the sum of the interior angles of a triangle is 180°:

180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 24° - 65° = 91°

So, d° = 65° + 91° = 156°

A shortcut to get this answer is to remember that angles around a line add up to 180°:

a° + d° = 180°
d° = 180° - a°
d° = 180° - 24° = 156°

Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

A rhombus is a parallelogram with four equal-length sides. A square is a rectangle with four equal-length sides.

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

-5a - 6 = \( \frac{a}{4} \)
4 x (-5a - 6) = a
(4 x -5a) + (4 x -6) = a
-20a - 24 = a
-20a - 24 - a = 0
-20a - a = 24
-21a = 24
a = \( \frac{24}{-21} \)
a = -1\(\frac{1}{7}\)