Question 897177
a+c=115,
7.5*a+3*c=678
a=115-c
7.5*(115-c)+3*c=678
862.5-7.5c+3*c=678
-4.5*c=-184.5
c=41.0
a=115-c
a=74 at 7.5 and  c=41 at 3
check
74+41=115
7.5*a+3*c=678
7.5*74+3*41=678
555.0+123=678
678.0=678
ok