sin(θ − ϕ);

Question

tan(θ) = 3/4,
θ in Quadrant III,
sin(ϕ) = − (3sqrt 10)/10,
ϕ in Quadrant IV

Answer 1

since tanθ = 3/4 in QIII,
sinθ = -3/5
cosθ = -4/5
since sinϕ = -3/√10 in QIV,
cosϕ = 1/√10
Now you have everything you need to evaluate sin(θ − ϕ)
using your formula.