Answer:
A = ± 
Step-by-step explanation:
Given
b²A² - 3g = q ( add 3g to both sides )
b²A² = q + 3g ( divide both sides by b² )
A² =
( take the square root of both sides )
A = ± 
GH: chord
M: point of tangency
MJ: diameter
J: center
MH: radius
GH: secant
200mm is the right answer
99 gallons it takes 3 1/3 gallons to water 1 plant then multiply 3 1/3*30