Hey there ! 
Let us take the length of the shorter piece as ' x ' 
Then, the longer piece would be ' 3 + 5x ' 
Total = 45 
x + 5x + 3 = 45 
6x + 3 = 45 
Subtracting 3 on both sides 
6x = 42
dividing by 6 on both sides 
x = 7
shorter wire = 7 ft 
longer = 45 - 7 
= 38 ft
Hope my answer helps!