we have
[tex]R=5(c/a-0.3)[/tex]
Solve for c--------> that means that clear variable c
so
Divide by [tex]5[/tex] both sides
[tex]R/5=(c/a-0.3)[/tex]
Adds [tex]0.3[/tex] both sides
[tex](R/5)+0.3=(c/a)[/tex]
Multiply by [tex]a[/tex] both sides
[tex]a[(R/5)+0.3]=c[/tex]
so
[tex]c=a[(R/5)+0.3][/tex]
therefore
the answer is
[tex]c=a[(R/5)+0.3][/tex]