Answer:
Mrs Gregory started with 1 litre of concentrated cleaner, which is equal to 1000 millilitres of cleaner. (we have to convert litre to millilitres because " she used 200 millilitres to clean her kitchen)
She mixed the 1000 millilitres of cleaner with 10 litres of water, which is equal to 10,000 millilitres of water. This gives a total of:
1000 + 10,000 = 11,000 millilitres of cleaner solution
She used 200 millilitres of the solution to clean her kitchen, which leaves:
11,000 - 200 = 10,800 millilitres of cleaner solution
To fill the 600-millilitre spray bottles, she needs to divide the total amount of cleaner solution by the amount of solution in each bottle:
10,800 / 600 = 18
Therefore, Mrs Gregory filled 18 spray bottles.