write it in R

Write a function called `gradeSummary` whose input `x` is a number. Your function will return a list with two elements, named `letter.grade` and `passed`. The letter grade will be `"A"` if `x` is at least `90`. The letter grade will be `"B"` if `x` is between `80` and `90`. The letter grade will be `"F"` if `x` is lower than `"80"`. If the student's letter grade is an A or B, `passed` should be TRUE; `passed` should be FALSE otherwise.