12.6

First make 0.051 to 51 and 0.6426 to 642.6

then divide 64 and 51 so you get 1 so 51×1=51

then 64-51=13 then bring down the 2 so you get 132 then divide 132 and 51, 132÷51=2... then 51×2=102

132-102=30 then bring down 6 so you get 306

306÷51=6

then 51×6=306 so 306-306=0 or x

12.6

thanks me later