a 3 degree polynomial has potentially 3 real zeroes.

Its local max and minimums can be found by taking the derivative

and setting it =0

3x^2+4x -13 = 0

x = -4 + or - sqr(16+169) all over 6

= -2/3 + or - (1/6)sqr185) = -.67 + or - 13.6/6 = -.67 + or - 2.3 = -3 or 1.63

-3 is a max and 1.63 is a minimum. the graph will cross the x axis somewhere above x=2

and possibly 2 other times when x<0

P(0) = -10

P(1) = -20

P(2) = -20

P(3) = -4

P(4) = 34

one zero is somewhere between x = 3 and x= 4, probably just a little over 3, maybe 3.1

the other two zeroes are on either side of x=-3

P(-4) = +10

P(-3)=-32

another zero is between -3 and -4, closer to -4, so maybe about -3.7

P(-2) = -35

P(-1)=+4 another zero is between -1 and -2, maybe about -1.1

that's a rough estimate, zeroes of 3.1, -1.1 and -3.7