[tex]\sf11 {x}^{2} - 3 {x}^{2} \\ [/tex]
They are like terms so you can just easily subtract them directly.
[tex]\sf11 {x}^{2} - 3 {x}^{2} \\ = \boxed{\bf8x {}^{2}} [/tex]
Hope it helps.
RainbowSalt2222
[tex]\\ \sf\longmapsto 11x^2-3x^2[/tex]
[tex]\\ \sf\longmapsto (11-3)x^2[/tex]
[tex]\\ \sf\longmapsto 8x^2[/tex]
