Evan washes two types of vehicles. It takes him 30 minutes to wash a car and 40 minutes to wash a truck. He charges $12 to wash a car and $15 to wash a truck. In 270 minutes, Evan made $105 washing cars and trucks. How many trucks did Evan wash?

Let c be the number of cars and t the number of trucks. The time and earnings give 30c + 40t = 270 and 12c + 15t = 105. Dividing these equations by 10 and 3, respectively, gives 3c + 4t = 27 and 4c + 5t = 35. Subtracting the first equation from the second gives c + t = 8; solving with 3c + 4t = 27 gives t = 3. Evan washed 3 trucks, choice B.

AI-written and checked against the verified answer.