Estimate decimals sums and differences

First basically solve.
Next, take the number after the decimal point and see if it's larger than 5 or lesser than 4.
Than, Look at the number before the decimal point and relate back to step 2 (Next) if the number is higher than one. Add by 1 to the number before the decimal.
Example:
4.45


4.(4)5 > The 4 is lesser than 4, so the number before the decimal point is keep the same.

4

Num of plants = (original#ofplants)*(1.6)^t