If tanθ = 3/4 and θ is acute, the value of (sinθ + cosθ)/(sinθ − cosθ) is:

Divide numerator and denominator by cosθ to get (tanθ + 1)/(tanθ − 1) = (3/4 + 1)/(3/4 − 1) = (7/4)/(−1/4) = −7. The sign matters: the denominator is negative because tanθ < 1.