a) Notam A = suprafata de teren
[tex] \frac{A}{4} [/tex] + 30 = suprafata cu porumb
[tex] \frac{5}{8} [/tex] · ( A - [tex] \frac{A}{4} [/tex] - 30 ) = suprafata cu grau
[tex] \frac{A}{4} [/tex] = suprafata cu orz.
A = [tex]\frac{A}{4} +30 + \frac{5}{8}*(A- \frac{A}{4} - 30 ) + \frac{A}{4} = \frac{A}{2} + 30 + \frac{5}{8}*( \frac{3A}{4} - 30) = [/tex]
[tex] \frac{A}{2} + 30 + \frac{15A}{32} - \frac{150}{8} = \frac{16A+960+15A-600}{32} <=>A=\frac{31A+360}{32} [/tex] <=>
32A = 31A + 360 => A =360 ha
b) Porumb : 360:4 + 30 = 90 + 30 = 120 ha
Orz : 360:4 = 90 ha
Grau : 360 - 120 - 90 = 150 ha