It should be 0.8
Note that here, we are asked to calculate average virtual address translation time. So the equation would be like this:
Let the hit rate be $x$.
$200 = x(100) + (1-x)(100+500)$.
Solving this should get you the value of $x$ as $0.8$.
Here, we don't add the time to access the page from the memory because we only care about the address translation time.