A=(-4)+(-21)=-4-21=-25
B=8-(-3)=8+3=11
C=12+(-18)=12-18=-6
D=(-4)-(-6)=-4+6=2
E=-8*(-5,2)=41,6
F=13*(-1,2)=-15,6
G=(5/8)+(1/4)=(5/8)+(2/8)=7/8
H=5-(3/7)=(35/7)-(3/7)=32/7
I=(-12/15)*(35/-36)=(-2*6*5*7)/(-3*5*2*3*6)=7/9
J=(5/8):(7/4)=(5/8)*(4/7)=(5*4)/(2*4*7)=5/14
K=(7/4)-(3/4)*(8/9)=(7/4)-(3*2*4)/(4*3*3)=(7/4)-(2/3)=(21/12)-(8/12)=13/12
L=((2/3)+1):((2/3)-1)=((2/3)+(3/3)):((2/3)-(3/3))=(5/3):(-1/3)=(5/3)*-3=-5
