I'm positive that it's rational
4*2/5 = 22/5
16*1/2 = 33/2
22/5 ............. 1 min
33/2 ..............x min
x = 33/2 : 22/5 = 33/2 x 5/22 = 165/44 = 3,75 min
If the value was initially v, then after a year it is 0.75v, after 2 years it’s 0.75²v, and so on. So after 6 years it’s 0.75⁶v.
So 0.75⁶v=7500, and v=7500/0.75⁶=$42,139.92 approximately. This is close to $42,140.