2x - 5y = P---(1)
4x - 7y = -28---(2)
-7x + 5y = -9---(3)
From (2), 28x - 49y = -196---(4)
From (3), -28x + 20y = -36---(5)
on adding, we get -29 y = 232
⇒ y = 232/-29 = -8
\(\therefore\) x = \(\frac{-28+7y}{4}=\frac{-28-56}4=-7-14=-21\)
\(\therefore\) P = 2(-21) - 5(-8) = -42 + 40 = -2