Answer:
6.9
Explanation:
 4v5 -2v3
set it equal to 0
 4v5 -2v3=0
Move all terms to the left side and set equal to zero. Then set each factor equal to zero. 
Exact Form: 
v = 0 , √ 2/ 2 , − √ 2 /2 
Decimal Form: 
v = 0 , 0.70710678 ... , − 0.70710678 
So, it would be 6.9