Step-by-step explanation:
Singer A's pay can be modelled using an expression which is linear in the number of hours she serves.
[tex]P_{a}(h)=45+10h[/tex]
Singer B's pay can also be modelled using an expression which is linear in the number of hours she serves.
[tex]P_{b}(h)=65+5h[/tex]
Both singers charge same amount when [tex]P_{b}(h)=P_{a}(h)[/tex]
[tex]45+10h=65+5h\\5h=20\\h=4[/tex]
∴ Both singers charge same amount at 4 hrs of service