If a : b :: 3 : 4 then the value of expression $$\frac{5a-3b}{7a + 2b}$$ is :​

Correct option is A

​Given:

​$$a : b = 3 : 4$$​​

Solution:

Let $$a = 3k$$​ and $$b = 4k$$​ (where k is a constant).

Expression: $$\frac{5a - 3b}{7a + 2b}$$​​

Substituting values of  a and b; 

$$\frac{5(3k) - 3(4k)}{7(3k) + 2(4k)}$$$$= \frac{15k - 12k}{21k + 8k}$$​  $$= \frac{3k}{29k}=\frac{3}{29}$$​​​