Dear student,

If the cube is painted externally, taking the number of sections made as ‘n’,
Number of faces with no colour = $\left(n-2{\right)}^{3}$
Number of faces with 1 colour = $6×\left(n-2{\right)}^{2}$
Number of faces with 2 colours =

Here, your n is 7. So number of 1 coloured faces will be $6×\left(n-2{\right)}^{2}=6{\left(7-2\right)}^{2}=6×{5}^{2}=6×25=150$