Sir Isaac Newton has shown us, in his _Universal Arithmetic_, that we may
divide the bullocks in each case in two parts--one part to eat the
increase, and the other the accumulated grass. The first will vary
directly as the size of the field, and will not depend on the time; the
second part will also vary directly as the size of the field, and in
addition inversely with the time. We find from the farmer's statements
that 6 bullocks keep down the growth in a 10-acre field, and 6 bullocks
eat the grass on 10 acres in 16 weeks. Therefore, if 6 bullocks keep down
the growth on 10 acres, 24 will keep down the growth on 40 acres.
Again, we find that if 6 bullocks eat the accumulated grass on 10 acres
in 16 weeks, then
12 eat the grass on 10 acres in 8 weeks,
48 " " 40 " 8 "
192 " " 40 " 2 "
64 " " 40 " 6 "
Add the two results together (24 + 64), and we find that 88 oxen may be
fed on a 40-acre meadow for 6 weeks, the grass growing regularly all the
time.