If the triangle on the grid below is translated by using the rule (x, y) > (x-2,y+2) what will be the coordinates of a'?

Cassie is traveling 675 miles today to visit her brother and his family. so far, she has stopped for gas three times. at the first stop, she put in 7.1 gallons of gas and paid $23.79. at her second stop, she put in 5.8 gallons of gas and paid $19.08. and, at the third stop, 6.6 gallons and paid $20.39. at which stop did casey pay the most for gas?

How do you find the area of a triangle

Can someone me with this problem i don't understand i need