(+2)-(+7)-(+11) = 2-7+11
(+12)-(+2)-(-12) = -12-2+12
(+12)-(+2)-(-12) = 12-2+12
(-25)-(-25)-(+2)-(-5)=3
(+15)-(-5)-(+20)-(-3)=15+5-20+3
(+15)-(+5)-(+20)-(-3) = -7
(+37)-(-24)-(+13)-(-6)=-54