Researchers are testing a new type of antibiotic. After administering a dose to a patient, they estimate that the amount of antibiotic in the patient's bloodstream will decrease by 26% every hour. If there are x milligrams of antibiotic in a patient's bloodstream after 2 hours, about how much will there be after 4 hours?
If the amount of antibiotic decreases by 26% every hour, then the amount remaining after each hour will be 100% - 26% = 74% of the previous amount.
So after 2 hours, there will be x * 0.74 * 0.74 = x * 0.5464 milligrams of antibiotic remaining.
After 4 hours, there will be x * 0.5464 * 0.74 = x * 0.4036 milligrams of antibiotic remaining.
Therefore, there will be about 0.4036 * x milligrams of antibiotic remaining after 4 hours. Answer: \boxed{0.4036x}.