Simultaneous equations -- with the variable upper limit of integration

I have the following two-equation system with two unknowns (a and b):

equation 1

\[ \frac{40000-1.1a^{0.91}40000^{0.091}}{200} - b = 0 \]

equation 2

\[ 640\pi \int_{0}^{b} t \left (\frac{40000-200t}{1.1a} \right)^{10} dt - 4000000 = 0 \]

In the second equation, b is the upper limit of integration that I have to solve for simultaneously. Someone advised me that I start with the 2nd equation to conduct 12-degree polynomial approximation. I wonder how to solve this problem with MATLAB. Thanks.