A) t=0 N = 3

B) sinus is minimum with the value -1, and maximum 1, so N is minimum at N=2*(-1)+3=1, and maximum N = 2*1+3 = 5

C) t=8 N = 2sin(pi*8/5)+3 = (calculator DRG to rad) = 1.097886...=1.100 thousends. Size is 1100

D) N = 4, 4-3=2sin(pi(t)/5) , 0.5 = sin(pi(t)/5) , use 0.5 sin-1, pi*t/5 = 0.523598..., t = 0.8333 weeks, 0.8333*7=5.8333. On the fifth day the population exceed 4000.