how to calculate the weight?

	Actual Volume	Budget Volume	Variance
ProductA	8	5	        60%
ProductB	20	15	        33%
Total	        28	20	        40%
	Actual Revenue	Budget Volume	Variance
ProductA	100	85	        18%
ProductB	400	350	        14%
Total	        500	435	        14.9%
	Actual Revenue/Volume	BudgetRevenue/Volume	      Variance   weight
ProductA	12.5	           17	                        -26%      X
ProductB	20	          23.33	                        -14%      Y
Total	       17.86	          21.75	                        -17.9%

My Questions is how can i calculate the weight(X and Y) for variance
of revenue/volume?
X and Y should satisfy the following equation :
-26%X+(-14%)Y=-17.9%

Isn't the answer simply the proportional weightings of product A and B?

If so, X+Y=1.
You already know that -26%X-14%Y=-17.9%

By using algebra:

14Y = 17.9 -26X
14Y = 17.9 - 26(1-Y)
12Y = 8.1

Y = 0.675

so X = 0.325

And just to check, (-26% x 0.325) + (-14% x 0.675) does equal -17.9%