Answer: Answer might be 4.2 kilograms per month
Step-by-step explanation: I know that the main pattern is 7.8 kilos in 1.5 months, so I divided that by three to get 3 0.5s ( 2.6 ) and added two of dems together for one solid 4.2 kilograms as a answer.
I don't know for sure ( just woke up ) but hope this helps!