diagonal
draw an immaginary line diagonal
now yo has right triangle
pythagorean theorem
if yo has a right triangle with legs legnth a and b and hypotonuse c (diagonal), then a^2+b^2=c^2
legs are 24 and 18
18^2+24^2=c^2
324+576=c^2
900=c^2
sqrt both sides
30=c
diagonal legnth=30 inches
