i need help ASAP 6th grade work!!!!! HELP

Answer:
y=7miles
Step-by-step explanation:
The total perimeter is 21 miles and we know two sides of the triangle are 7 miles, or 14 miles together.
We need to know the one other side of the triangle, so we can subtract the 14 miles we know from the total 21 miles.
21-14=7miles
Answer:
y=7 mi
Step-by-step explanation:
If you know that each side of this triangle is 7 and they are each side is the same length, you can make an educated guess that the answer is 7. If you need An easier method 7x3=21. a triangle has 3 sides so your answer would be 7