Solution :
Number of days = 90 days
Amount invested = $45 million
So the current earnings is [tex]$\$45 \text{ million } \times 1.075 \text{ in}\ \ 90 \text{ days}$[/tex]
The number of days is reduced to 50 days. So we can now make the same amount in just 50 days.
So the net increase is what we will make in the remaining [tex]40[/tex] days.
If in 50 days, we earn 0.075 return, then we can consider 50 days as [tex]t=1.[/tex]
Then the [tex]50[/tex] days = [tex]45 \times 0.075^1[/tex] return, and
[tex]40[/tex] days = [tex]45 \times (0.075)^{40/50}[/tex]
[tex]=45 \times (0.075)^{4/5}[/tex]
= [tex]\$ 5.66580371[/tex] million increase
= $ 5.7 million