Let n = the unknown number.
Six times a number = 6 * n = 6n
20 more than number = n + 20
Greater than = >
Put it all together:
6n > n + 20
Subtract n from both sides to get constants on one side and variables on the other:
6n - n > 20
5n > 20
Divide both sides by 5 to isolate variable N
n > 4
or (4, ∞)