Answer:
a. about 187 feet
b. about 19 trees
c. about 228 dollars
What we know:
a. Find the perimeter of the field. about 187 feet
solve for the missing side length ('x'):
add all side lengths:
b. You are going to plant dogwood seedlings about every ten feet around the field's edge. How many trees do you need? about 19 trees
c. If each dogwood seedling sells for $12, how much will the trees cost? about $228