let the substance other than silica and water in the original clay be 'y'.let percent of silica in original clay be x. then x+y=100-12=88 implies y=88-x----(1)

in the final mixture x'=50 ; x*p=x'=50  .y*p=y'=43  (where p is some constant and will be same for both x&y because their fractional increase in percent will be same ) implies x/y=50/43

x/88-x =50/43 ,on solving x=88*50/93=47.31

therefore the percent of silica in original clay is 47.31