#### Answer

$$595350 \mathrm{N}$$

#### Work Step by Step

Since
$$
\frac{\Delta y}{\sin 30^{\circ}}=2 \Delta y
$$
and the area of each strip is
$$
A=(3)(2)(\Delta y)=6 \Delta y
$$
Therefore,
\begin{aligned}
F=\rho g \int_{a}^{b} y f(y) d y &=9800 \int_{6}^{7.5} 6 y d y \\
&=9800\left[3 y^{2}\right]_{6}^{7.5} \\
&=9800[168.75-108] \\
&=9800[60.75] \\
&=595350 \mathrm{N}
\end{aligned}