Question 191781
let  y=  -10x^2  -6x  +4^3  =   -10x^2  -6x  +64

at  y=0,   0= -10x^2 -6x +64

0=  10x^2+6x-64
0=2(5x^2 +3x -32)

use  quadratic  eqn  to  solve

x= ( -(3)  +-  (  (3)^2 - 4 (5) (-32) )^1/2  )  /  2 (5)

x=(  -3  +- (  9+640)^1/2 ) /10

x=(-3 +-25.5) / 10

x=+2.25,  (-2.85)

check

ok  using  calc