If they all painted at the same rate the equation is this
mothers 8
daughters 12 at 220 sq ft
mothers 6
daughters 8 at 152 sq ft
220 +152 =372 divided by 34 (because they all painted at the same rate)=10.94 sq ft they each painted
The direction vector of the line
L: x=1+t, y=4t, z=2-3t
is <1,4,-3>
which is also the required normal vector of the plane.
Since the plane passes through point (-5,9,10), the required plane is :
Π 1(x-(-5)+4(y-9)-3(z-10)=0
=>
Π x+4y-3z=1
The dimension will be x(7x+1) centimetres squared