When planning his crops, farmer sue knows that her 15 acres can support apples and pecans. she wants to make $8,500 from her crops. she can make $1,050 per acre of apples (the variable a) and $2,500 per acre of pecans (the variable p). which equation below would be a constraint in her system of equations?
a)1,050a + 2,500p = 8,500
b)a + p = 15
c)a - p = 15
d)2,500p - 1,050a = 8,500

(I don't know this, I googled the problem and it opened the answer on openstudy, so I copied and pasted it to here)
ok...
    they say that the total Sue expects from her crops is = $8500
 
and
    she gets $1050 per acre from apples... if she grows "a" acres then her outcome will be
                                  1050a
   
she gets $2500 per acre from pecans if she grows "p" acres then the outcome will be
                                  2500p
 
but since her total is 8500
          1050a + 2500p = 8500 (1)
             21a + 50p = 170 (1)

since her land area is 15 acres
                a + p = 15 (2)
 
so.. ur choices will contain one out of the followings..
 
hope this will help ya :)