Judging from the meaning of the question: in △ABC, ∠ cab = 90-60 = 30,

∠ABC=90 +30 = 120

Then ∠ c = 180- 120-30 = 30.

So △ABC is an isosceles triangle, where AB=BC=20.

The speed of ship B is 20÷0.5=40 knots.

∫AC = 2×√( 20？ - 10? )=20√3

∴ The speed of ship A is 20√3÷0.5=40√3 knots.

If you don't understand, please ask. . .