Start by finding to total amount of the tip:
[tex]Tip = rate * base[/tex]
[tex]T=rb[/tex]
[tex]T=25\%\times$65[/tex]
[tex]T=0.25\times65[/tex]
[tex]T=$16.25[/tex]
And then add the two together: $65 + $16.25 = $81.25
You can also do it another way by realizing that in total they payed 125% of what the dinner cost:
[tex]Total=125\%\timescsot[/tex]
[tex]T=1.25c[/tex]
[tex]T=1.25\times65[/tex]
[tex]T=$81.25[/tex] same as above.
