(14) 3x+(-4x)-(+6x)= (15) 2x+(+5x)-(-8x)= (16) -5a-(-6a)-(+2a)= (17) a-3a-(-7a)= (18) (1)/(2)a-(1)/(3)a-(1)/(4)a= (19) -x+(x)/(3)-(x)/(9)= (2)/(3)a-(+(5)/(6)a)-(-(1)/(2)a)=

(14) $3x+(-4x)-(+6x)=-7x$<br />(15) $2x+(+5x)-(-8x)=15x$<br />(16) $-5a-(-6a)-(+2a)= -a$<br />(17) $a-3a-(-7a)=5a$<br />(18) $\frac {1}{2}a-\frac {1}{3}a-\frac {1}{4}a=\frac {1}{12}a$<br />(19) $-x+\frac {x}{3}-\frac {x}{9}=-\frac {5}{9}x$<br />$\frac {2}{3}a-(+\frac {5}{6}a)-(-\frac {1}{2}a)=\frac {1}{6}a$