Answer:
5 or -8
Step-by-step explanation:
[tex](3 \times x) + x {}^{2} = 40[/tex]
[tex]3x + {x}^{2} = 40[/tex]
[tex] {x}^{2} + 3x - 40 = 0[/tex]
using factorization method
[tex]( {x}^{2} + 8x) ( - 5x - 40) = 0[/tex]
[tex]x(x + 8) - 5(x + 8) = 0[/tex]
[tex](x - 5)(x + 8) = 0[/tex]
[tex]x - 5 = 0[/tex]
or
[tex]x + 8 = 0[/tex]
[tex]x = 5[/tex]
or
[tex]x = - 8[/tex]
