Express the given statements as an equation:
a) 13 subtracted from twice of a number gives 3.
b) One-fifth of a number is 5 less than that number.
c) A number is 7 more than one-third of itself.
a) 2n - 13 = 3
b) (1/5)n = n - 5
c) n = (1/3)n + 7