To find the area of a triangle, you can use the formula:
\[ \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} \]
In this case, the base of the triangle is 7.5 centimeters and the height is 4 centimeters. Plugging those values into the formula gives:
\[ \text{Area} = \frac{1}{2} \times 7.5 , \text{cm} \times 4 , \text{cm} \]
Calculating this:
\[ \text{Area} = \frac{1}{2} \times 30 , \text{cm}^2 = 15 , \text{cm}^2 \]
So the area of the box lid is 15 square centimeters.