Question 102217
{{{ 2.1x + 45.2 = 3.2 - 8.4x }}}
Firstly, you can arrange the equation so one side will have the variables and the other constants.

{{{ 2.1x + 8.4x = 3.2 - 45.2 }}}
{{{ 10.5x = -42 }}}
{{{ x = -42/10.5 }}}
{{{ x = -4 }}}

Hope that helps :)