Question 191759
.14  S  + .07   C  =   .10  *280  

but  s + c  =280,    therefore  let  c=280-s

.14  S  +.07  (  280-S)  =  28

.14 S  + 19.6  -.07 S  =  28

.07  S  =  8.4

S=120

and  c=  280-120 = 160

check

.14  (120)  +  .07  (  160)  =  28

16.8  +  11.2  =  28      ok