algebra

To find x divide 21 by 3 then to find y divide 21 by 6

The answer is that x & y axes intercepts is when the respective values are 0.

So for the X axis intercept the y value will be
3*0 - 6y = 21
y = -21 / 6

Similarly for Y axis intercept, the x value will be
3x - 6*0 = 21
x = 21 / 3

Hope that helps