Question 186630
Let x be tons of fertilizer. Let y be acres of land.
Cost of Fertilizer is given by 200x.
Cost of Land is given by 2000y
The total cost is given by
{{{TotalCost = CostOfFertilizer + CostOfLand}}}
{{{20000 = 200x + 2000y}}}

That equation is a line
{{{graph(400,600, -10, 140, -10, 20, -0.1x + 10)}}}

The portion of the line that is 'a real answer' in this case, requires that both fertilizer and land be positive values. So use that part of the curve  bounded by
x>=0 and x<=10.