I'm in an intro to stats class right now, and have absolutely no idea what's going on. How would I solve the following problem using R?

Let x be a continuous random variable that has a normal distribution with a mean of 71 and a standard deviation of 15. Assuming n/N is less than or equal to 0.05, find the probability that the sample mean, x-bar, for a random sample of 24 taken from this population will be between 68.1 and 78.3,

I'm really struggling on this one and I still have to get through other problems in the same format. Any help would be greatly appreciated!