13) -4= -b -1/3b and -23/3= 1/2a + 5/3a

-4=-1b-(1/3)b
-4=-(4/3)b
-4/-(4/3)=b
b=3
-------------------------------
(1/2)3+(5/3)2
3/6+10/6=13/6
-23/3=13/6a
(-23/3)/(13/6)=a
a=-46/13