These questions are really algebra questions related to the core concept in DS that if the number of variables equals the number of equations you can solve the problem.
Here you have 3 triangles and one straight line (QRS)- and you have 5 variables - (angle Q, QRS, RPQ, RPS, SRP - we know that s=90) Each triange has a formula that says the sum of its angles =180 and the line says the sum of its angles is also 180. Therefore you have 5 variables and 4 formulas - all you need to be able to solve is one more formula.
each of the answer choices gives you an additional formula so each is sufficient on its own - Answer D (by the way I've seen this problem with 7 triangles and it is the exact same problem.)
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA