What is the Magnitude of Acceleration in the n Direction?

[goldfish9776]

Homework Statement

can someone tell me why the acceleration in n direction is 18ms^-2 ? i only understand that the centripetal acceleration = 18ms^-2

Homework Equations

The Attempt at a Solution

 

[kotone]

I think your question is answered in the second image, in the text above. It's simply plugging the centripetal acceleration into the equation for net force. :P