Question 762578
Ratio of yellow to green initially is 4:7.

Assume there were 4*x yellow balls, which means that there were 7*x green balls.

6 green balls removed. So number of green balls now is 7*x - 6
3 yellow balls added. So number of yellow balls now is 4*x + 3

After this change, it is given that the number of green balls and yellow balls are equal.

Hence {{{7*x - 6) = (4*x + 3)}}}

Solve for x. Adding 6 to both sides, and subtracting 4*x from both sides,

{{{3*x = 9}}} or {{{x = 3}}}

Yellow balls = 4*x. Green = 7*x.

Hence number of yellow balls = {{{highlight(12)}}} and number of green balls = {{{highlight(21)}}}

:)