One crew can seal a parking lot in 12 hours and another in 15 hours. how long will it take to seal the parking lot if the two crews work together?

This is a typical work problem in algebra. The approach to this is using the equation: Rt = 1, where R is the rate per person working, t is the amount of time worked by an individual. All their rates must equal to 1. The solution is as follows:

12/x + 15/x = 1
Solving for x,
x = 27 hours

So, if they work together, they can finish the work in 27 hours.

X^2 - 4x +(4/2^2) + y^2 + 8y + (8/2^2) = -4 + (4/2^2) + (8/2^2)(x + 2)^2 + (y + 4)^2 = -4 + 4 + 16your center is (-2, -4) and the radius is the sqrt of -4 + 4 + 16 which is 4

This does not make sense