Choose the correct answer of the following question:

As, the sides of the triangle are $20 \mathrm{~m}, 21 \mathrm{~m}$ and $29 \mathrm{~m}$

So, the semi $-$ perimeter $=\frac{20+21+29}{2}=35 \mathrm{~m}$

Now, the area of the triangular field $=\sqrt{35(35-20)(35-21)(35-29)}$

$=\sqrt{35 \times 15 \times 14 \times 6}$

$=\sqrt{7 \times 5 \times 5 \times 3 \times 7 \times 2 \times 2 \times 3}$

$=2 \times 3 \times 5 \times 7$

$=210 \mathrm{~m}^{2}$

$\therefore$ The cost of cultivating the field $=210 \times 9=₹ 1890$

Hence, the correct answer is option (c).