Me i usually know how to do this but i idk what i am doing wrong

Well,  we know the dimensions, width is "x" and lenght is "x+1"
area is A = l * w, so we know the area is 30

thus 30 = (x+1)x



well, the width can't be -6, so it has to be 5

Ais the correct answer

Hope this ; )