There is only one solution
It would be: 567/18 = 31.5
So, she needs atleast 32 shelves....
3x-5y=4------eq1
4x+3y=15-------------eq2
multiply 3 to first eq and 5 to second eq.
9x-15y=12
20x+15y=75
subtract both eqs
29x=87 x=3 so put x in eq 1
3(3)-5y=4
5y=5
y=1