If $$\frac{x+a}{x+b} = \frac{x+3a}{x+a+b}$$​,find the value of ‘x’.

Correct option is D

Given: 

​$$\frac{x+a}{x+b} = \frac{x+3a}{x+a+b}$$ 

Solution:  

​$$\frac{x + a}{x + b} = \frac{x + 3a}{x + a + b} \\ \ \\(x + a)(x + a + b) = (x + b)(x + 3a) \\ \ \\x^2 + xa + xb + ax + a^2 + ab = x^2 + 3ax + bx + 3ab \\ \ \\-ax - 2ab + a^2 = 0 \\ \ \\x = a - 2b$$​​