Answer
$$640\ kg.$$
Work Step by Step
The lever principle states that
$$F_1d_1=F_2d_2.$$
To find $d_1$, we subtract the fulcrum distance from the lever length to obtain:
$$d_1=3.65-0.45=3.2\ m$$
Then we plug in the given values to get:
$$ 90\times 3.2=x\times 0.45\Longrightarrow x=\frac{ 90\times 3.2 }{0.45}=640\ kg.$$
