A worker's present salary is N24,000 per annum and his annual increment is 10% of his basic salary. 

This means that at the beginning of the second year, his salary will increase by 10% of N24,000, which is N2,400. 

So, his salary at the beginning of the second year will be N24,000 + N2,400 = N26,400. 

At the beginning of the third year, his salary will again increase by 10% of his basic salary.

Since his basic salary at the beginning of the second year was N26,400, his increment at the beginning of the third year will be 10% of N26,400, which is N2,640. 

So, his salary at the beginning of the third year will be N26,400 + N2,640 = N29,040.