How can we isolate the variable c

Well depending on the equation you look at both sides and eliminate everything from both using addition, subtraction, multiplication, and division.

Ex:

3c-4=7 first add the 4 because you use the opposite type of operation so you add it to 7 which gives you:

3c=11 next you have to divide to get it alone

3c/3=11/3

which gives you

c = 3.66666666667