Let x rep. numbers of boys that can work at $\frac{5}{4}$ the rate at

which the 10 girls work
or 1 hrs, x boys will work for $\frac{\frac{1}{5}\times 10}{4}$

x = $\frac{5}{4}$ x 10

= 8 boys

8 boys will do the work of ten girls at the same rate

4 + 8 = 12 bous cut the field in 5 hrs for 3 hrs,

$\frac{12\times 5}{3}$ boys will be needed = 20 boys.