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Can someone please help me solve the following 3 problems on GMAT PowerPrep Practice Test #1: #7: Data sufficiency - Determining magnitude of difference between 2 angles in 2 triangles #15: Arithmetic - If each term in the sum a1+a2+...+an is 7 or 77 and the sum equals 350, which of the following could be equal to n? (Answer 40) #18: Problem solving - Function f(x)=f(1-x) I cannot figure these out for the life of me. Thanks:hmm: