A nichrome wire for a heater is 1.8 m long, with a diameter of 0.45 mm…

Step 1. The area. $r = 0.225 \times 10^{-3}\ \text{m}$, so $A = \pi r^2 = 1.59 \times 10^{-7}\ \text{m}^2$.

Step 2. The resistance. $R = \dfrac{1.1 \times 10^{-6}\ \Omega\,\text{m} \times 1.8\ \text{m}}{1.59 \times 10^{-7}\ \text{m}^2} = 12.4\ \Omega$.