Concept:Use the identity cosθ=sin(90∘−θ) to equate the two sine expressions.Explanation:Given: sin(5x−28)∘=cos(3x−50)∘Rewrite cos(3x−50)∘ as sin[90∘−(3x−50)∘].So, sin(5x−28)∘=sin(140∘−3x).Equate the angles: 5x−28=140−3x.Solve: 5x+3x=140+28.Thus, 8x=168.Hence, x=21.Answer:x=21, so the correct option is C.