Answer:
2.4 hours
Step-by-step explanation:
David's time = 6 hours
Anthony's time = 4 hours
the combined time is given by the following formula
1/ (david's time) + 1/(anthony's time) = 1/total time
1/6 + 1/4 = 1/Total
4/24 + 6/24 = 1/Total
10/24 = 1/ total (taking reciprocal of both sides)
24/10 = total
total time = 24/10 = 2.4 hours
Answer:
degrees.
Step-by-step explanation:
Line ABC is a straight line, and the angle on a straight line is always 180 degrees.
Since ABD + DBC = ABC, we know that 

Divide both sides by 9:

DBC is
degrees.
If you use the first answer, the equation becomes 2x + 2y = 16. You could subtract this from equation Q to eliminate x.
The second answer makes equation P -2x - 2y = -16. You could add this to equation Q to eliminate x. You can use both of these methods to eliminate the x term, but if you can only choose one, you should choose the second option.