Afarmer finds that he can buy 5 sheep and 5 cows for $129or 10 sheep and 17 cows for $177 .how much will it cost him to buy 3 sheep and 2 cows

Let the cost of one sheep and one cow be x and y respectively.
Therefore,

5x+5y=129
10x+17y =177

Solving the two equations,
Multiply the first equation by 2 and subtract the second from the results;
10x+10y = 258
10x+17y = 177
0x-7y = 81 => y= $-11.57 (cannot be a negative value). The details of the question need to be checked.

Now,
5x+5y = 129 => 5x-57.86 =129=>5x = 186.86 => x= $37.37