#### Answer

She must plant 85 acres of pumpkins and 335 acres of corn

#### Work Step by Step

Let p=acres of pumpkin and c=acres of corn
Based on the problem, we have equations:
p+c=420
c=p+250
Substitute value of c into the first equation: p+(p+250)=420
Simplify, 2p+250=420
Subtract 250 from both sides: 2p=170
Divide 2 from both sides: p=85
Plug in p to find c: 85+c=420 => c=335