x=number of roses
y=number of prunes
we can suggest this system of equations:
x+y=255
x=2y+15
We can solve this system of equation by substitution method.
x=2y+15
(2y+15)+y=255
3y=240
y=240/3
y=80
x=2y+15
x=2(80)+15
x=160+15
x=175
Answer: there was 175 roses and 80 prunes.