On a blueprint with a scale of 1cm = 2ft, the length of a wall is 12cm. if the scale of the blueprint were 1cm = 3ft, what will be the length of the wall? ( show work, i will mark brainliest)

I will assume that this question asks for the length of the wall on the new blueprint. It is not worded nicely.
The actual length of the wall is
                               12 cm * (2 ft / 1 cm) = 24 ft
On the new blueprint of 1 cm = 3 ft, the length on blueprint becomes
                                24 ft * (1 cm / 3 ft) = 8 cm
The length of the wall on the new blueprint is 8 cm.