I am having a lot of trouble solving this problem.

A satellite that is 4175 miles from the center of the earth, orbits with a period of 90 minutes. What is its centripetal acceleration?

I converted 4,175 mi into 6,717,575 m and 90 min into 5,400 sec.

For V_{T }I got 7,816.25 m/sec.

And A_{c}= 49,111 mi/sec^{2}

Help? I have no clue what I'm doing.