Answer
The magnitude of the resultant force is 533.5 N
Work Step by Step
Let $a = 250~N$
Let $b = 450~N$
Let angle $\theta = 85^{\circ}$
We can use the parallelogram rule to find $c$, the magnitude of the resultant force:
$c = \sqrt{a^2+b^2+2ab~cos~\theta}$
$c = \sqrt{(250~N)^2+(450~N)^2+(2)(250~N)(450~N)~cos~85^{\circ}}$
$c = \sqrt{284610.04~N^2}$
$c = 533.5~N$
The magnitude of the resultant force is 533.5 N