Complete the following series.
e25, j100, o225, ?​​

Given: e25, j100, o225, ?

Logic: Letter is increasing + 5 and number is increasing perfect square of 5, 10, 15 and 20.

For, letter

e + 5 = j, j + 5 = o, o + 5 = t

For, number

5²= 25, 10²= 100, 15²= 225, 20²= 400

So, the missing term is t400.

Thus, correct option is (a).