What is the total area of the house and garage and the cost to maintain the lawn?

$$
\text{Area of House} = \text{length} \times \text{width} = 15 \text{ m} \times 10 \text{ m} = 150 \text{ m}^2
$$

$$
\text{Area of Garage} = \text{length} \times \text{width} = 5 \text{ m} \times 4 \text{ m} = 20 \text{ m}^2
$$

$$
\text{Total Area} = 150 \text{ m}^2 + 20 \text{ m}^2 = 170 \text{ m}^2
$$
The total area of the house and garage is $\boxed{\text{170 m}^2}$.

$$
\text{Total Property Area} = \text{length} \times \text{width} = 40 \text{ m} \times 20 \text{ m} = 800 \text{ m}^2
$$

The property is a rectangle with a length of $40 \text{ m}$ and a width of $20 \text{ m}$.

$$
\text{Perimeter} = 2 \times (\text{length} + \text{width})
$$
$$
\text{Perimeter} = 2 \times (40 \text{ m} + 20 \text{ m})
$$

$$
\text{Perimeter} = 2 \times (60 \text{ m}) = 120 \text{ m}
$$
The perimeter of this property is $\boxed{\text{120 m}}$.