Transform hex to decimal in excel

col\row   | 0    | 1   |
------------------------
       A  | 0x123| 291 |

From 0x123 to 291

step 1. remove "0x" : =RIGHT(A0, LEN(A0)-2)
step 2. use "HEXTODEC" : =HEXTODEC(RIGHT(A0, LEN(A0)-2))

From 291 to 0x123

step 1. use "DECTOHEX" : =DECTOHEX(A1)
step 2. add prefix "0x": =CONCATENATE("0x", DECTOHEX(A1))