The function is often written y=Asin(kx) where A is the amplitude, and k determines the frequency at which the function oscillates.
The amplitude is defined as the maximum change in the function from the y=0 position, which occurs when the sin function equals one. For this to happen, the multiplier must be 7. So, in answer to the first part of the question, we can rule out choices (c) and (d), as these have only half the designated amplitude.
The frequency can be trickier. Knowing that the sin function repeats its cycle every time the argument in brackets goes through a multiple of 2pi, we look for the one that will give us the result 2pi when xgoes from 0 to 4pi. This will be the one with (x/2) in the bracket. When x=0, (x/2) also equals zero. But x=4pi will be the next time that (x/2) will equal 2pi, and the function will complete one cycle.
