@harryyour, already got it but let me just prove to you that your method of solvin is more convincing than the initial.
[size=20]The product of the HCF & LCM of numbers= The
product of those numbers..
Let the unknown number be 'Z'
I.e. 15x180 = 60xZ
2700= 60Z.
***Divide Both Side by 60.***
45= Z.
.'. The missing number is 45.[/size]