I think Mr. Han is around the 60 or 70 age.
I am really sorry that I couldn't answer this problem. Try starting with 21 and multiply that by 3. To check if you can do it, add 43 to the number you multiply 3 with. Again, i am really sorry that i only wrote a hint. Good luck finding the answer!
Given:
square with sides measuring 7 cm.
3 triangles attached to three sides of the square. A line bisecting one triangle is measured at 4 cm.
Area of a square = s² = (7cm)² = 49 cm²
Area of a triangle = hb/2 = (4cm*7cm)/2 = 14 cm²
Area of the 3 triangles = 14 cm² x 3 = 42 cm²
Total area of the logo = 49 cm² + 42 cm² = 91 cm²
Let , side lawn is a.
Area of boundary is :

Now, total cost is given by :

Area left is :

Price to empty space with turfs is :

Therefore, the cost of covering the empty space with turfs at the rate of Rs 20 per sq. metre is Rs 262500.
Hence, this is the required solution.
Consider this option:
C³₂₇=27!/(3!*24!)=25*13*9=2925 ways to select 3 students.
B^-2/ab^-3 = b^-2/b^-3 x 1/a = b^[-2-(-3)] x 1/a = b x 1/a = b/a