Algebra 1

$40$ mi/hour
Given: $\dfrac{980}{450+s}=\dfrac{820}{450-s}$ Apply cross multiplication. $820(450+s)=980(450-s)$ $410(450+s)=490(450-s)$ $184500+410s=220500-490s$ $410s+490s=220500-184500$ $900s=36000$ Thus, $s=\frac{36000}{80}$ Hence, $s=40$ mi/hour