Find the scale from the 6 inch height of the triangle on the car to the 30 ft height on the building:
30 feet = 30 x 12 = 360 inches.
360 inches / 6 inches = 60
The scale is 60
Now multiply the base of the triangle on the car by 60 to get the distance of the car from the building:
15 inches /12 inches = 1.25 feet
1.25 feet x 60 = 75 feet.
The car was 75 feet from the building.