To solve this you would make a triangle, Assuming you had a piece of paper.
It would look like the picture included (where ever that is) sorry for the horrible drawing with mouse.
You can then you Pythagorean Theorem to solve this
[tex] a^{2} + b^2 =c^2[/tex]
width will be (a)
put in your variables
[tex]a^2 + 72^2 = 90^2[/tex]
[tex]a^2 + 5184 = 8100[/tex]
Subtract 5184 over and get
[tex]a^2 = 2916[/tex]
square root both sides and get
a=54
the field is 54 meters wide
