Correct option is (D) 23
Let labourer works x number of days and absent y days.
\(\because\) Total number of days he engaged = 30
\(\therefore\) x+y = 30 ___________(1)
Labourer earned Rs. 735 in total.
\(\therefore\) 35x - 10y = 735 ___________(2)
Put y = 30 - x from (1) into (2), we get
35x - 10 (30 - x) = 735
\(\Rightarrow\) 35x - 300 + 10x = 735
\(\Rightarrow\) 45x = 735+300 = 1035
\(\Rightarrow\) x = \(\frac{1035}{45}\) = 23
\(\therefore\) y = 30 - x = 30 - 23 = 7 (From (1))
Hence, number of days he worked is x = 23.