please help this probability and stat questions, thank you

The test score of an English test is normally distributed with a mean of 55 and a standard deviation of 10.

a) What is the probability that a randomly selected student will score between 45 and 70. (4 marks)

b) If the bottom 25% student is required to attend remedial class, what is the cut-off score for selecting students to attend the class?(6 marks)