let the length be 'L'
L = 1+b (given ) ---- (i)
area = L* b
given area as 3 3/4 (mixed fraction ) = (3*4 + 3) / 4 = 15 / 4
from (i)
area = (1+b)* b = b+ b*b
b^2 +b = 15 /4
4b^2 +4b = 15
solving the quadratic equation
b = 3/2 or -5/2
as breadth can't be negetive
the breadth is 3 / 2