Let [tex]a[/tex] be the number of hours worked at Job A and [tex]b[/tex] the number of hours at Job B. Then
[tex]a+b=30[/tex]
and
[tex]7.5a+8b=234.50[/tex]
From the first equation,
[tex]b=30-a[/tex]
and substituting this into the second gives
[tex]7.5a+8(30-a)=234.50\implies-0.5a+240=234.50[/tex]
[tex]\implies0.5a=5.50[/tex]
[tex]\implies\boxed{a=11}[/tex]
