Explanation

Let Maryum's current age be x.

Ten years ago, Maryum's age was x - 10.

After one year, Maryum's age will be x + 1.

According to the problem, after one year, Maryum's age will be two times her age ten years ago:

x + 1 = 2(x - 10)

Now, simplify the equation:

x + 1 = 2x - 20

Add 20 to both sides:

x + 21 = 2x

Subtract x from both sides:

21 = x

So, Maryum's current age is 21.