Look at the figure shown below: A triangle RPQ is shown. S is a point on side PQ, and T is a point on side PR. Points S and T are joined using a straight line. The length of PS is equal to 28, the length of SQ is equal to 12, the length of PT is equal to x, and the length of TR is equal to 15.

Patricia is writing statements as shown below to prove that if segment ST is parallel to segment RQ, then x = 35:

Statement Reason
1. Segment ST is parallel to segment QR. Given
2. Angle QRT is congruent to angle STP. Corresponding angles formed by parallel lines and their transversal are congruent.
3. Angle SPT is congruent to angle QPR. Reflexive property of angles
4. Triangle SPT is similar to triangle QPR. Angle-Angle Similarity Postulate
5. ? Corresponding sides of similar triangles are in proportion.

Which equation can she use as statement 5?
x:15 = 28:40
28:12 = x:(x + 15 )
x + 15 = 28 + 12
28:40 = x:(x + 15)