Final answer:
Annie and Whitney will reach a page count of 6 when they start typing together.
Step-by-step explanation:
To find the page count that Annie and Whitney will reach when they start typing together, we need to compare their rates of typing.
Annie types 3 pages per hour, so if she types for x hours, she will type 3x pages.
Whitney types 1 page per hour, so if she types for x hours, she will type x pages.
They have already typed 4 and 8 pages respectively, so the equation becomes: 3x + 4 = x + 8.
Simplifying the equation, we get 2x = 4, which means x = 2.
Therefore, when Annie and Whitney start typing together, they will both reach a page count of 6.