how do I Solve for c: 6/15=2/c

This is a proportion so

6/15=2/c

make the left side top number equal to the right side top number and you will find c

6/15=2/c

6/3=2

6/15 times (1/3) / (1/3) = 2/5

2/5=2/c

c=5

the other way is multiply both sides by c/2

6c/30=1

multiply both sides by 30

6c=30

divide both sides by 6

c=5