Question 705584
This is like a mixture problem.  Let x amount hours of the helper and y the hours of the florist.


8*x+12*y=320  accounting for dollars.
x+y=30  account for hours.


Divide the dollars equation by 4.
2*x+3*y=80


The system is as simple as
2*x+3*y=80
x+y=30

Subtract 2 times the second equation from the first equation:
0*x+1*y=20
y=20 hours for the florist.