The scientist has to take x ounces of the solution A and B of the solution B, so that
[tex]x+y=110[/tex]The amount of salt S this solution has is
[tex]S=0.6x+0.85y[/tex]Since we need a solution with 75% salt, then we need that
[tex]\begin{gathered} \frac{S}{110}=0.75 \\ \frac{0.6x+0.85y}{110}=0.75 \\ 0.6x+0.85y=82.5 \end{gathered}[/tex]Then, we have the system of linear equations
[tex]\begin{gathered} x+y=110 \\ 0.6x+0.85y=82.5 \end{gathered}[/tex]Solving for x in the first equation and replacing in the second
[tex]\begin{gathered} x=110-y \\ 0.6(110-y)+0.85y=82.5 \\ 66-0.6y+0.85y=82.5 \\ 0.25y=16.5 \\ y=66 \\ x=110-66=44 \end{gathered}[/tex]Then, if we take 44 oz of A and 66 of B we have
[tex]0.6(44)+.85(66)=82.5[/tex]In conclusion, the scientist needs to take 44 oz of the solution A and 66 oz of solution B.