[tex] \left \{ {{x - y = 1.50} \atop {40x + 40y = 940}} \right.
\\ \\
*x - y = 1.50[/tex]
x = 1.50 + y
*40x + 40y = 940
40 (1.50 + y) + 40y = 940
60 + 40y +40y = 940
60 + 80y = 940
80y = 940 - 60
80y = 880
y = 880/80
y = 11
*x - y = 1.50
x - 11 = 1.50
x = 1.50 + 11
x = 12.5
x=DAVID
Y=PETER
