Answer:
The area is the product of length and width.
.. area = length * width
.. 61 5/8 = (7 +7 1/2) * width
.. (61 5/8)/(14 1/2) = width = 4 1/4 . . . . feet
The plywood was 4 feet 3 inches wide.
A calculator that works with fractions figures this nicely. By hand, you might compute it as
.. 61 5/8 = (8*61 +5)/8 = 493/8
.. 14 1/2 = (2*14 +1)/2 = 29/2
.. (61 5/8)/(14 1/2) = (493/8)/(29/2) = (493/8)*(2/29) = 493/(4*29) = 493/116
.. 493/116 = 4 +29/116 = 4 +29/(4*29) = 4 1/4
