The boiling point of water at sea level is 212 degrees Fahrenheit (${}^{\circ}$F). For every 550 feet above sea level, the boiling point of water is lowered by about 1${}^{\circ}$F. Which of the following equations can be used to find the boiling point $B$ of water, in ${}^{\circ}$F, $x$ feet above sea level?