Math
posted by Ciara .
Carlo drove for 3 hours in a fog, then increased his speed by 30 miles per hour (mph) and drove 6 more hours. If his total trip was 540 miles, then what was his speed in the fog.

Let x = the mph for the first three hours.
540 = 3x + 6(x + 30)
540 = 9x + 180
360 = 9x
40 = x