ANSWER:
Part A: c. 240 Hz
Part B: 4 loops
Explanation:
Given:
String length =20 cm = 0.2 m
When there are two loops, the length of the string is equal to the wavelength, therefore
Wavelength (λ) = 0.2 m
Speed (v) = 48 m/s
Part A:
We can calculate the frequency using the following formula:

The frequency is equal to 240 Hz, so the correct answer is c. 240 Hz
Part B:
We can determine the frequency when the number of loops is doubled knowing that these are proportional, as shown in the following figure:
This means that if the frequency is doubled, the number of loops is doubled, therefore, there will be 4 loops (2*2)