So for the first three months, she spent 72% of her salary, which means she spent .72*1800 = $1296 each month for the first three.
But now we need to know how much she spent per month for the last 4 months.
The clue here is that she SAVED 25% more per month, so now we have to ask, how much did she save per month for the first three?
The answer is 1800-1296 = $504
Now we know she saved 25% more than that, which comes out to be 1.25*504 = $630
Which means she SPENT 1800 - 630 = $1170 per month for the last 4 months
So now we get that the average is: (3*1296 + 4*1170)/7 = $1224