we are given
c=9 is a solution
we will select each options and then verify it
option-A:
[tex]4-c=5[/tex]
Subtract both sides 4
[tex]4-c-4=5-4[/tex]
[tex]-c=1[/tex]
Multiply both sides by -1
[tex]-c*-1=1*-1[/tex]
[tex]c=-1[/tex]
so, this is FALSE
option-B:
[tex]20=14+c[/tex]
Subtract both sides by 14
[tex]20-14=14+c-14[/tex]
[tex]6=c[/tex]
so, this is FALSE
option-C:
[tex]15=c-6[/tex]
Add both sides by 6
[tex]15+6=c-6+6[/tex]
[tex]21=c[/tex]
so, this is FALSE
option-D:
[tex]\frac{c}{3} =3[/tex]
Multiply both sides by 3
[tex]3*\frac{c}{3} =3*3[/tex]
[tex]c =9[/tex]
so, this is TRUE
