Account A pays 4.04% simple interest and Account B pays x% interest compounded semiannually. The interest earned from a principal of $10000 from both accounts at the end of the first year is equal.
Quantity A
x

Quantity B
3.8

I solve it as follows :

since 10K in both is P I cancel It.
I am left with

(4.04/100)=(x/4)^2
X=40%

May someone clarifies what is the mistake in my solution ?