Can someone explain the elimination method to me for this problem?

Find the sum of 4x^{2} -4+6 and -7^{2} +3x+1

Anew test for ra is being developed. the test is administered to 750 patients with ra and 750 without ra. for the sake of the question, assume the prevalence of ra in this population is 50%. of the 750 patients with ra, 575 have a positive result. of the 750 patients without ra, 150 have a positive result. what is the positive predictive value of the new test? a575/(575+150) b. 600/(600+ 150) c. 575/(575+125) d. 600/(600+ 125)

2f(x)= x+3 if 4 < x < 8 2x if x 28 2