Floating point results in Bash integer division

Just double-quote (") the expression:

echo "$a / ( $b - 34 )" | bc -l

Then bash will expand the $ variables and ignore everything else and bc will see an expression with parentheses:

$ a=22
$ b=7
$ echo "$a / ( $b - 34 )" 
22 / ( 7 - 34 )

$ echo "$a / ( $b - 34 )" | bc -l
-.81481481481481481481