The amplitude is basically the distance between the max and min values of the function (values of y) divided by two. Sine gets as large as 1 and as small as -1, so it's amplitude is 1. Any coefficient multiplied by sine is thus the new amplitude. In this case, the amplitude is .25 (the function is being amped by .25, in this case it is reduced by 75%)

The period deals with the x-axis, and it is the range of values it takes for the function to complete one rotation of its pattern. For sine, the function curves up then down and back up to the x-axis. Normally, the period for is . In this case, x-values are divided by four, so the period would have to be four times the usual amount or .