I need help with this question thank you!

3) According to High Rollers Inc, 75% of the time a loaded pair of dice (meaning dice are biased) will land so that the sum will be seven. The dice are rolled 400 times. a) Describe the sampling distribution of p, the sample proportion of rolling a sum of seven. (i.e. What is the sampling distribution of p?) b) What is the probability that at least 72% of the rolls of the loaded dice will result in a sum of seven