Answer
5 years ago about 133.9 million tax returns were filed.
Work Step by Step
We know that 51%, or 68.3 million, tax returns were filled electronically. We can use this fact to find out the total number of tax returns filed with a proportion:
$\frac{51}{100}=\frac{68.3}{x}$
We cross-multiply:
$51*x=100*68.3$
$51*x=6830$
$x=6830/51$
$x=133.9$ million
Thus 5 years ago about 133.9 million tax returns were filed.
