A tennis instructor chargers $40 for each one hour lesson and $25 for each half hour lesson if the instructors I come from 35 lessons was $1115 how many one hour lessons did she give?

X = 1 hr lessons and y = 1/2 hr lessons

x + y = 35 ... y = 35 - x

40x + 25y = 1115

40x + 25 (35 - x) = 1115

40x + 875 - 25x = 1115

40x - 25x = 1115 - 875

15x = 240

x = 240/15

x = 16 < = = = there are 16 one-hr lessons

and 19 half-hr lessons