Let x and y be the original costs of tie and belt, respectively. Then the after sale prices will be
Tie: (1-0.2)x= 0.8x
Belt: (1-0.3)y= 0.7y

Now, we need to find the percent reduction on the total cost of 1 tie and 2 belts. Remember,

Percentage decrease= 100*(Base value - Final Value)/Base Value

Here, we have Base value= x+2y
Final value= 0.8x +2(0.7)y= 0.8x+1.4y

Percentage decrease= 100*(x+2y-0.8x-1.4y)/(x+2y)=100*(0.2x+0.6y)/(x+2y)

Note that the percent decrease value depends on the values of x and y (i.e. original cost of tie and belt). Hence, the relationship cannot be determined and the answer is D.