A heater is made of nichrome wire 0.30 mm across…

Step 1. The area. $A = \dfrac{\pi d^2}{4} = \dfrac{\pi \times (0.30 \times 10^{-3}\ \text{m})^2}{4} = 7.07 \times 10^{-8}\ \text{m}^2$.

Step 2. The length. $L = \dfrac{RA}{\rho} = \dfrac{15\ \Omega \times 7.07 \times 10^{-8}\ \text{m}^2}{1.0 \times 10^{-6}\ \Omega\,\text{m}} = 1.06$ m.

Step 3. The turns. One turn is $\pi D = \pi \times 0.020\ \text{m} = 0.0628$ m. So $N = \dfrac{1.06\ \text{m}}{0.0628\ \text{m}} = 16.9$, about $17$ turns.