Question 446334
Let {{{x}}} = cost of 3 books before tax
{{{ x + .07x = 22.5 }}}
{{{ 1.07x = 22.5 }}}
{{{ x = 22.5/1.07 }}}
{{{ x = 21.03 }}}
The tax was 
{{{ .07x = .07*21.03 }}}
{{{ .07*21.03 = 1.47 }}}
The tax was $1.47 for 3 books