Hey there! :)
You have to find 10% of 450 and add it to 450 to get the amount he will read the next month. Then, add that with 450 to get the total
10% = 0.1
0.1 × 450 = 45
450 + 45 = 495
He will read 495 next month
This month + next month = 495 + 450
495 + 450 = 945
He will read 945 minutes in the next 2 months
:)