how to solve this?

Numbers are 12/4 and 15/4

LCM = 60/4 = 15

i) The given two numbers in rational form are: (3/1) & (15/4)

ii) LCM of rational numbers = (LCM of numerators)/(HCF of denominators) = 15/4
[LCM of 3 & 15 is 15; HCF of 1 & 4 is 4]

Thus LCM is 3.75

The LCM of two integers a and b, usually denoted by LCM(a, b), is the smallest positive integer that is divisible by both a and b. Applying the same reasoning to 3 and 3.75 (even though 3.75 is not an integer) the LCM is 3.75 since it is divisible by both 3 and 3.75. If you want an integer solution, you must multiply 3.75 by 4 to get rid of the decimal fraction. In this case the LCM is 15, which is divisible by both 3 and 3.75 to yield an integer in both cases.

In case of num which has no factor other than 1 as in,
3=3×1 and 3.75×1=3.75.
L.c.m= 3×3.75=11.25.