Answer:
A good rule is to change 10 to 15 percent of the water each week. If your tank is heavily stocked, bump that up to 20 percent each week. A lightly stocked aquarium can maybe get by for two to four weeks, but this should be the maximum length of time between water changes.
Step-by-step explanation:
This is the correct answer you want
Please follow me
(b - 4z)/7 = a
b - 4z = 7a
b = 7a + 4z
Answer: b = 7a + 4z