Question: Inputting double integrals correctly for 2 variable functions

I have a question where I'm trying to find the value of some variable C that when multiplied by the double integral of a function returns 1 as the answer.

The function I'm in putting is f:=(x,y) -> C* exp((-0.001*x)-0.002*y), but leaving out the C when inputting into maple

The function also has parameters for the values of x and y where both are between -1 and 1(including =1 and 1) and x<y with x being greater than or equal to 0

I need to take the double integral under these parameters but I can't for the life of me input the double integral of the function that will return me a value and not return a solution that still has an x or a y in it

The same goes for trying to isolate the values of F(x) in terms of y and f(y) in terms of x using the integral with these parameters so that

f(x) = int( f(x,y)dy and f(x) = int(f(x,y)dx