If the mean of the following distribution is 2.6,

Consider the following table.

Now,

mean $=\frac{\sum f x}{\sum f}$

$\frac{2.6}{1}=\frac{28+3 y}{12+y}$

$31.2+2.6 y=28+3 y$

$3 y-2.6 y=31.2-28$

$0.4 y=3.2$

$y=\frac{3.2}{04}$

$y=8$

Hence, the correct option is (b).