Let the origin be at the center of the window
$\displaystyle F = w \int_c^d h(y) \cdot L(y) \, dy$
$w$ is the weight-density of the fluid = $64 \, lb/ft^3$
$h(y)$ is the depth of a representative horizontal strip of window = $100-y$
equation of the circular window is $x^2 + y^2 = 1 \implies x = \sqrt{1-y^2}$
$L(y)$ is the length of a representative horizontal strip of window = $2x= 2\sqrt{1-y^2}$
$\displaystyle F = 64 \int_{-1}^1 (100-y) \cdot 2\sqrt{1-y^2} \, dy$