Even without doing the math, (and without having the requisite diagram to view), it seems likely that the rectangle was simply divided along the diagonal. And, if that's the case then the two triangles formed would have the same area. So, if one triangle's area ABC is 600 sq. yds. as the problem states, then the other triangle ACD also would be 600 sq. yds.
But if we do the math anyway, we can get the same result.
Keep in mind that:
P of rectangle = 2 ( l + w)
A of rectangle = (l x w)
A of triangle = h x b divided by 2
I'd say that the length of the rectangle is 40 and the width is 30.
P of rectangle is 2 (30 + 40) = 140 .... check
A of rectangle is 30 x 40 = 1,200 .... check
A of triangle is 30 x 40 divided by 2 = 600 ...... check
