Answer: $262.50
Step-by-step explanation:
The yards are sized in a ratio of 4:5.
Assuming the perimeter of both farms is x, the formula to calculate it will be;
[tex]\frac{4}{4 + 5} x = 280\\\\x = 280/\frac{4}{9} \\\\x = 630 yards[/tex]
The perimeter of the larger fence will therefore be;
= 630 - 280
= 350 yards
The cost to dig the trench will be;
= 350 * 0.75
= $262.50