We have the equation
y = Asin (Bx)
The amplitude = A = 4
Finding B is a little tricky.....we want to solve this :
2pi / Period = B
2pi / [ 3pi / 2 ] = B
4pi / 3pi = B
(4/3) = B
So...the equation becomes
y = 4sin (4/3 x)
Here's the graph for one period : https://www.desmos.com/calculator/ncw51ksw5x