For an equilateral triangle of side $l = 1$ m, the perpendicular distance from centre to each side:
$$a = \frac{l}{2\sqrt{3}} = \frac{1}{2\sqrt{3}}$$

Each side subtends $\phi_1 = \phi_2 = 30°$ at the centre.
$$B_{side} = \frac{\mu_0 I}{4\pi a}(\sin 30° + \sin 30°) = \frac{\mu_0 I}{4\pi a} \cdot 1$$

$$B_{total} = 3 \times \frac{\mu_0 I}{4\pi a} = 3 \times \frac{4\pi \times 10^{-7} \times 10}{4\pi \times \frac{1}{2\sqrt{3}}}$$
$$B_{total} = 3 \times 10^{-6} \times 2\sqrt{3} = 6\sqrt{3} \times 10^{-6} \approx 1.04 \times 10^{-5} \text{ T}$$