The phrase "We have ... of financial problems" refers to a large quantity or number of financial problems.
"Lots" is the correct word as it refers to a large number of something.
Thus, the correct choice is "lots."
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?