One possible way of estimating an answer to see if it is a realistic solution is rounding up/down numbers with decimals so you can easily guess!
For example, in this problem, lets round 1.8 up to 2 and 16.5 up to 17.
2 × 17 = 34
34 is not that far from 29.7 !
So, we can say that 29.7 is a realistic solution considering the inclusions of decimals.