Plumber and his assistant work together to replace the pipes in an old house . the plumber charges $45 per hour for his own work and $25 for his assistant's labor. the plumber works twice as long as his assistant on this job, and the labor charge on the final bill is $4035. how long did the plumber and his assistant work on the job?

$45 per plumber hour (p)
$25 per assistant hour (a)
$4035 = 25a + 45p
p = 2a

4035 = 25a + 45(2a)
4035 = 25a + 90a
4035 = 115a
a = 35.086 hours
p = 2(35.086)
p = 70.174 hours

The plumber worked about 70 hours, and his assistant worked about 35 hours.

Using "h" to represent the height and "i" as the number of inches the city is falling after each year, we can construct an equation. We know that the city begins at -72 inches, as it is that far below sea level. After one year, it drops (2*1) inches, or 2 inches after that first year. After two years, the fall would be (2*2) inches, or 4 inches. Thus, the full equation would be "h = -72 - 2i".