A coal mine worker is 650 feet below the ground in a mine. Another coal mine worker is 7 feet above ground operating machinery.

The first coal mine worker is 650 feet below, so they're -650 ft.

The second coal mine worker is 7 feet above, so they're +7 ft.

| -650 | = 650 ft

| 7 | = 7 ft

650 > 7, so the first worker is farther from the surface.

use this formula:

p(a\b) = p(a and b)/p(b).

take it from here.

what is the original number? you forgot to add it.