Let's start with a word equation.
The point when both people begin reading the SAME page, we know that both people have read the same number of pages
So we can write: number of pages Bob has read = number of pages Jane has read

Given: Bob starts reading at 4.30 pm, and Jane starts reading at 5.20 pm
In other words, Bob is given a 50-minute head start (aka a head start of 5/6 hours).
So, if we let t = the amount of time, in hours, Jane spent reading, then....
t + 5/6 = the amount of time, in hours, Bob spent reading (since Bob gets to read for an additional 50 minutes)

Output = (rate)(time)
Substitute values into the original word equation to get: (30)(t + 5/6) = (40)(t)
Expand the left side to get: 30t + 25 = 40t
Subtract 30t from both sides of the equation: 25 = 10t
Solve: t = 25/10 = 2.5

In other words, Jane's reading time = 2.5 hours.
Since Jane began reading at 5:20, the time at which they were both reading the same page = 5:20 + 2.5 hours = 5:20 + (150 minutes)

Answer: 150