he needs to make at least 63.5m of fencing (this will be 64m to the nearest metre).

each plank is at least 13.5cm long (this is 14cm to the neares cm).

can you finish?

Note: it is also possible to interpret the question as "he needs to be able to make 64.5m of fencing". The question is ambiguous so you will just have to pick one interpretation.