A task has an early start of day 4.

The float (or slack) in a project management context is calculated as the difference between the late start and the early start (or late finish and early finish). In this case:

Float=Late Start−Early Start=14−4=10 days\text{Float} = \text{Late Start} - \text{Early Start} = 14 - 4 = 10 \text{ days}Float=Late Start−Early Start=14−4=10 days

So, the correct answer isB. 10.