.

Solution: In the integral y is held fixed and x ranges from 3y to 3:

When the order is reversed x is held fixed on the interval [0,3] and y ranges from 0 to x/3.

Evaluating the reversed integral:

Maple Check:

int( int( exp(x^2), y = 0..x/3), x = 0..3);

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by: gm
**