I have revision questions that i have not completed in 7+ years. Needing some help prior to my exam. How would you answer this question?

a)
LR² = SL² + SR² + 2 * SL * SR * cos∠LSR (cosine law)
LR² = 4000² + 5000² - 2 * 4000 * 5000 * cos60° m²
LR = 4583 m

b)
SR / sinϕ = LR / sin∠LSR (sine law)
5000 / sinϕ = 4580 / sin60°
sinϕ = (5000/4583) * sin60°
ϕ = 70.9°

c)
∠LSR + ∠SLR + ∠RLS = 180° (∠ sum of Δ)
60° + 70.9° + δ = 180°
δ = 49.1°

d) i)
Denote the buoy as M.

In ΔSRM :
cos45° = MS / (5000 m)
MS = 5000 * cos45° m
MS = 3536 m
The required distance = 3536 m

d) ii)
If the complete event means from S to M, then to R, the shortest distance = 5000 m

If the complete event means from S to M, then to R, then to S, the shortest distance = 0 m