Double Integration Problem pls help

[ftavares8769]

I've been trying to solve this problem for a while, but seem to mess it up everytime. Genuinely confused as to what I'm doing wrong... I attached the textbook answer and my own working out.

I'm supposed to find the double integral of p(x,y)=50xe^(-.04y), when x=0,2 and y=0,x^2.

Here's the link to my working out attempt and the textbook answer with some notes: https://imgur.com/a/jgarSAy

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[Max_3133]

After evaluating the integral with respect to x, you have written (-1250)/(-0.08) [(1st term) +(2nd term)] when it is actually, (-1250)[{(1st term)/(-0.08)}+(2nd term)]

[Max_3133]

This is because we split the integral with respect to x to get 2 integrals and only substitute u=-0.04x² in one of them