Mr. Chatwala harvested 51.43 kg of apples last year.
Let's denote the number of apples harvested last year as 'x'.
This year, the harvest increased by 75% compared to last year. This means the total harvest this year was 175% of last year's harvest.
Therefore, we can set up the equation:
1.75x = 90
To find the value of x, we can divide both sides of the equation by 1.75:
x = 90 ÷ 1.75
x = 51.43 kg
Therefore, Mr. Chatwala harvested 51.43 kg of apples last year.