ABCD is a quadrilateral. If m

ANSWER
A. 9
EXPLANATION
The sum of the measures of the interior angles of a quadrilateral is 360. In this case, we know that angles A and D are right angles, so their measures are 90°. Also, the measure of angle B is 99° and the measure of angle C is x², so we can write an equation for x,
[tex]90+90+99+x^2=360[/tex]Combine like terms,
[tex]279+x^2=360[/tex]Subtract 279 from both sides,
[tex]\begin{gathered} 279-279+x^2=360-279 \\ \\ x^2=81 \end{gathered}[/tex]And take the square root of each side,
[tex]\begin{gathered} \sqrt{x^2}=\sqrt{81} \\ \\ x=9 \end{gathered}[/tex]Hence, the value of x is 9.