Answer:
The width of the field is 35 meters. 
Explanation:
Recall that the perimeter of a rectangle is given by: 

Where w is the width and l is the length of the rectangle. 
We know that the perimeter is 150 meters. Thus: 

Divide both sides by two: 

We are given that the length is five meters longer than the width. So: 

Substitute: 

Combine like terms: 

Subtract five from both sides: 

And divide both sides by two. Hence: 

Thus, the width of the rectangular field is 35 meters.