LCM-8 ("Mike Boat") is a river boat and mechanized landing craft used by the United States Navy and Army during the Vietnam War and subsequent operations.
If you mean 5 and 8 then the LCM is 40
If you mean 17 and 13 then the LCM is 221
If you mean: 8, 20 and 12 then the LCM is 120
If you mean 15, 12, 10 and 60 then the LCM is 60
If you mean: 49, 28 and 14 then the LCM is 196
If you mean an inflatable boat - sure
To work out the LCM, you need two numbers. You have provided only one so you can't work out the LCM.
It is spelled U-Boat not you-boat.
If you mean: 14 and 62 then the LCM is 434
If you mean 18 and 36 then the LCM is 36
If you mean 4 and 28 then the LCM is 28
If you mean 7 and 14 then the LCM is 14
If you mean 12 and 48 then the LCM is 48
If you mean 5 and 8 then the LCM is 40
If you mean 17 and 13 then the LCM is 221
If you mean: 24, 72 and 144 then the LCM is 144
If you mean: 10, 15 and 30 then LCM is 60