The degree of trinomial ax5−bx4+c is
Let P(x) = x6 + ax5 + bx4 + cx3 + dx2 + ex + f be a polynomial such that P(1)=1; P(2)=2; P(3)=3; P(4)=4; P(5)=5; P(6)=6 then find the value of P(7).