If the arithmetic mean of x, x + 3, x + 6, x + 9, and x + 12 is 10, the x =

The given observations are x, x + 3, x + 6, x + 9, and x + 12.

$\therefore \sum x=5 x+30, n=5, \bar{X}=10$

Now,

$\bar{x}=\frac{\sum x}{n}$

$10=\frac{5 x+30}{5}$

$50=5 x+30$

$5 x=20$

$x=4$

Hence, the correct option is (d).