In right triangle ABC, BC \equal{} 5, AC \equal{} 12, and AM \equal{} x; MN⊥AC, NP⊥BC; N is on AB. If y \equal{} MN \plus{} NP, one-half the perimeter of rectangle MCPN, then:
[asy]defaultpen(linewidth(.8pt));
unitsize(2cm);
pair A = origin;
pair M = (1,0);
pair C = (2,0);
pair P = (2,0.5);
pair B = (2,1);
pair Q = (1,0.5);draw(A--B--C--cycle);
draw(M--Q--P);label("A",A,SW);
label("M",M,S);
label("C",C,SE);
label("P",P,E);
label("B",B,NE);
label("N",Q,NW);[/asy] (A)\ y \equal{} \frac {1}{2}(5 \plus{} 12) \qquad (B)\ y \equal{} \frac {5x}{12} \plus{} \frac {12}{5}\qquad (C)\ y \equal{} \frac {144 \minus{} 7x}{12}\qquad
(D)\ y \equal{} 12\qquad \qquad \,\, (E)\ y \equal{} \frac {5x}{12} \plus{} 6 geometryrectangleperimeter