You're starting with 200 kg of berries, and 99% of that is water.
Since they're 99% water, that means that there's 1% of solid matter.
1% of 200 kg means that there are 2 kg of solid matter.
Some of the water evaporates in the sun, but the solid matter doesn't.
So there still remains 2 kg of solid matter.
Since the new water content is 90%, that means that now the solid matter is 10%.
So 2 kg (the solid matter) is 10% of the total weight.
And if 10% of the total weight is 2 Kilograms, If you multiply that by 10, you get the answer,
20 kilograms
