The solution for your problem.
Before install the following in ubuntu 64: sudo apt-get install libxtst6:i386
and then: sudo dpkg -i spark_2.6.3.12555-2_amd64.deb
The solution for your problem.
Before install the following in ubuntu 64: sudo apt-get install libxtst6:i386
and then: sudo dpkg -i spark_2.6.3.12555-2_amd64.deb