A:b=3:4 maka (6a+b):(4a+5b)=

[tex] \frac{a}{b} = \frac{3}{4} \\ a = \frac{3}{4} b[/tex]
maka,
[tex] \frac{(6a + b)}{(4a + 5b)} = \frac{(6 \times \frac{3}{4}b )+ b }{(4 \times \frac{3}{4}b) + 5b } \\ \frac{(6a + b)}{(4a + 5b)} = \frac{ \frac{18}{4}b + \frac{4}{4} b }{ \frac{12}{4} b + \frac{20}{4} b}[/tex]
[tex]\frac{(6a + b)}{(4a + 5b)} = \frac{ \frac{22}{4}b }{ \frac{32}{4} b} \\ \frac{(6a + b)}{(4a + 5b)} = \frac{22}{32}[/tex]
[tex]\frac{(6a + b)}{(4a + 5b)} = \frac{11}{16} [/tex]


jadi jawabannya adalah 11/16