To solve this equation, we first need to find a common denominator for all the fractions involved. In this case, the least common multiple of 3, 4, 9, and 20 is 180.

Rewriting the equation with the common denominator of 180:

(120/180) - (80/180) + (9/180) = (144/180)

Combine like terms:

(49/180) = (144/180)

To isolate the variable x, we need to multiply both sides of the equation by the reciprocal of the coefficient of x (180/49) on both sides:

(180/49) (49/180) x = (180/49) (144/180)

x = 144/49

Therefore, the solution to the equation is x = 144/49.