Given below the arrangement of loading on the larger boat by two tug boats.
F₁ = 5 N
F₂ = 4 N
Angle between them θ = 90⁰
Resultant between two vectors, 
Substituting

So magnitude of the net force on the block = 6.403 N
Your lungs aren’t the ones that make the sound
Answer:
Increasing the tension on a string increases the speed of a wave, which increases the frequency (for a given length). Pressing the finger at different places changes the length of string, which changes the wavelength of standing wave, affecting the frequency.
Explanation: