First, let's calculate how much money he saves each month, by calculating 30% of £400:
[tex]\frac{30}{100}\cdot400=30\cdot4=120[/tex]He saves £120 each month.
So, to reach the value of £600, the number of months needed is:
[tex]\frac{600}{120}=5[/tex]Therefore it will take 5 months to save enough money.