On the freeway, it is unsafe to drive too slowly or too quickly. The safest driving speeds on the freeway near Allan's town were scientifically determined to be between the minimum and maximum speeds (in miles per hour) according to the equation lx-551 42. Which equation can be used to determine the maximum safe driving speed?
X-55=4.2
X-55=-4.2
X+55=4.2
X+55=-4.2