if b=15 and c=6700 and b= 17 and c=7500 what is c if b=0

let c=mb+a

then 6700=m*15+a
and 7500=m*17+a

subtract the first from the second
800=2m or m=400

and 6700=400*15+a so a=6700-6000=700

so, if b is zero
c=400*0+700=700