How do I show variance in an equation for example if lets say the margin of error is .3 how do I express that in an expression? Do I for example do: 4.2 ± .3 to represent it?

When a 757 passenger jet begins its descent to the ronald reagan national airport in washington, d.c., it is 3900 feet from the ground. its angle of descent is 6 degrees. how far must the plane fly to reach the run way? a. 37,106 ft b. 37,310.4 ft c. 23,456.6 ft d 2,492.7 ft