Cost to run an Arduino device 24/7, simple maths question
It looks right.

\$ P = VI = 12 \times 0.025 = 0.3 \ \text W \$.

\$ E_{daily} = Pt = 0.3 \times 24 = 7.2 \ \text {Wh} \$.

\$ E_{annual} = 7.2 \times 365 = 2,628 \ \text {Wh} = 2.6 \ \text {kWh}\$

\$ Cost_{Annual} = 2.6 \ \text {kW} \times 27.56\ \text{c/kWh} = \text {AUD }0.72 \$.