just need the last part

Affine Cypher Define an encryption function f as below. f(P) (3p + 17) mod 26 . Use this function to encrypt the message "BEWARE OF ROGUE MANDRILLS . Find the decryption function and use it to decrypt the message "WMD APTXQDWD ADTKDORAHT RQD HE WHLHZ" [Include both the decryption function and the decrypted message in your report.] An affine cipher, in general, uses a function of the form f(p) (ap + b) mod 26 with ged(a, 26) 1. The message below was encrypted with some affine cypher. Can you crack the code and find the function that encrypted it? [Include both the encryption function and the decrypted message in your report.] "SRVYLOYBV VNY BELYRVNYQYQ TYHSFYLU VWRSINV