/*  Balanced HDD free space  */
max1 : 365.72$ Free1 : 208.47$
max2 : 99.99$ Free2 : 76.71$
sizeBy : solve((max1-Free1)/(max1+x)=(max2-Free2)/(max2-x), x)$
max1 + subst(sizeBy,x); max2 - subst(sizeBy,x);