Question 960927
The perimeter is the distance around the rectangular field, so you have two lengths and two widths:
2L+2W= P In this problem:
2L+2W= 300 
The problem also says the length equals W+50, so now we have:
2(W+50)+2W= 300 Multiply on the left to get rid of the parenthesis
2W+100+2W= 300 Now add W's on left and subtract 100 on both sides:
4W= 200 Divide both sides by 4
W= 50 The width is 50 and the length 50+50=100
Check P(300)= 2L+2W; P(300)= 2(100)+2(50); P(300)= 200+100 We have the correct answer.