In basketball, the number of points you score is given by 3x + 2y + 1z where x is three-pointers, y is two-pointers, and z is free throws (one-pointers).
What is the total number of points scored by a player who makes 3 three-pointers, 5 two-pointers, and 6 free throws?
You can just replace x, y and z using 3, 5 and 6. So the score gotten by the player is 3*3+2*5+1*6=25. So the total number of points scored by the player is 25.