Help please?

(a)
Refer to the figure below.
P₁ and P₂ are the initial and final positions of P.
Q₁ and Q₂ are the initial and final positions of Q.

In ΔP₂P₁Q₂:
Final distance between the two runners, D(t)
= P₂Q₂
= √(P₂P₁² + P₁Q₂²)   (Pythagorean theorem)
= √{(2.5t)² + [50 - 3.0(t - 1)]²} km
= √{(2.5t)² + (53 - 3.0t]²} km
= √(6.25 + 2809 - 318t + 9t²) km
= √(15.25t² - 318t + 2809) km

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(b)
Distance between two ships, s(t)
= √(AB² + AC² - 2×AB×AC×cos120°)   (cosine law)
= √[(32t)² + (15t)² - 2×(32t)×(15t)×cos120°)] knots•hours
= 41.6t knots•hours