On a number line, a number, b, is located the same distance from 0 as another number, a, but in the opposite direction. the number b varies directly with the number a. for example b = 2b equals 2 and startfraction 3 over 4 endfraction. when a = –2a equals negative 2 and startfraction 3 over 4 endfraction.. which equation represents this direct variation between a and b? b = –a –b = –a b – a = 0 b(–a) = 0