There would be four rows of 5. If he added one more row of desks he would have 25 desks.
Each line is a desk
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To find the length of the ladder, you need to do Pythagorean theorem.
50^2 + 30^2 = x^2
2500 + 900 = x^2
x^2 =3400
x= square root of 3400
58.31 OR 10 root34
To find the angle:
tan theta = opposite/adjacent
50/30 = 5/3
theta = tan inverse of 5/3
= 59.04