the variables are just the letters, in this case "x" and "y", and the coefficients are just the numbers in front of them, 75 and 25.
a term is a group that's delimited by a + or a -, so we have two terms here, 75x and 25y.
she makes $25 for dog-walking
1 job.............. 25(1)
2 jobs...........25(2)
3 jobs...........25(3)
x jobs............25x
now, the pizzeria earnings, she makes $75 a shift
1 shift...........75(1)
2 shifts.......75(2)
x shifts........75x.