Given triangle ABC. Angle C = 90 degrees, angle B = 60 degrees, and side AB = 18cm. Find the side of the speaker.

According to the condition of the problem, one of the acute angles is known, the second acute angle is equal to:
∠ А = 90 ° – ∠ В = 30 °.
The BC leg is located opposite ∠ A = 30 °, which means that half of the hypotenuse AB, BC = 9 cm.
The second leg AC is found by the Pythagorean theorem:
AC = √ (AB² – BC²) = √ (324 – 81) = √243 = 9√3 (cm).
Answer: The length of the speaker side is 9√3 cm.