Hi, I have a function for expected utility (EU) below:

EU=0.95(1000000-40000x)^(0.5) + 0.05(250000+750000x-40000x)^(0.5)

I need to solve for the value of x which maximises EU, I have differentiated with respect to x and set equal to zero but keep getting the wrong answer

can anyone help me with this? the right answer is 0.836, i don't know why im finding this difficult as it should be simple.

Thanks

Mark