This is a case of ratios
The bat population was 2,500,000 and at that time they were consuming 40 tons of insects. An increase in the bat population would lead to an increase in their insect consumption. If the population increases to 4,000,000 then the insect consumption would increase as follows;
[tex]\begin{gathered} \text{Ratio of bats to insect consumption;} \\ \frac{2500000}{40}=\frac{4000000}{x} \\ \text{Where x shows the amount of tons of insect that 4 million bats would consume} \\ \text{Cross multiply and you now have;} \\ 2500000x=4000000\times40 \\ x=\frac{(4000000\times40)}{2500000} \\ x=\frac{160000000}{2500000} \\ x=64 \end{gathered}[/tex]