Present age of Babu is 6 times of the present age of Ballu. Four years hence, Babu age will be 5 times of Ballu’s age. Find the age of Babu after 15 years.

The correct answer is 111 years.

Let us solve this step-by-step by formulating algebraic equations based on the given information.

Step 1: Define variables and set up the present age relationship.
Let the present age of Ballu be $x$ years.
According to the problem, the present age of Babu is 6 times the present age of Ballu.
Therefore, the present age of Babu = $6x$ years.

Step 2: Express ages after 4 years.
Four years hence (in 4 years):
Ballu's age will be = $x+4$ years.
Babu's age will be = $6x+4$ years.

Step 3: Set up the equation for the condition given after 4 years.
We are given that 4 years hence, Babu's age will be 5 times Ballu's age.
$6x+4=5(x+4)$

Step 4: Solve for $x$.
Expand the right side of the equation:
$6x+4=5x+20$

Subtract $5x$ from both sides:
$6x-5x+4=20$

$x+4=20$

Subtract 4 from both sides:
$x=16$

So, the present age of Ballu is 16 years.

Step 5: Find the present age of Babu.
Present age of Babu = $6x=6\times 16=96$ years.

Step 6: Calculate Babu's age after 15 years.
Age of Babu after 15 years = $96+15=111$ years.

Thus, the age of Babu after 15 years will be 111 years.