The diagram below shows rectangle RSTU with two diagonals drawn.
R
(6x-15)
63°
U
T
To find the value of x, Justin wrote the following steps.
1. mZSTR +m/RTU = 90°
2. mZRTU = 27"
3.6.1 15 = 27
4.62 = 42
5. = 7
Which statement can be used to justify the first step?
O The alternate interior angles formed by the diagonals are congruent.
The angles at each vertex of the rectangle are right angles.
Opposite angles in a rectangle are congruent.
The diagonals of a rectangle are congruent.