She can solve 75 questions per hour.
Solution:
Given that, a lady can solve 100 math problems every 4/3 hours.
We have to find how many math problems does she can solve per hour?
Now, according to the given information.
In [tex]\frac{4}{3}[/tex] hours ⇒ 100 problems
Then, 1 hour ⇒ "n" problems
So, by chris cross method.
[tex]\frac{4}{3} \times n = 1 \times 100[/tex]
[tex]\frac{4}{3}n = 100[/tex]
[tex]n = \frac{3}{4} \times 100\\\\n = 3 \times 25 = 75[/tex]
Hence, she can solve 75 questions per hour.