Question 1163456
 {{{R=4x+(x+5)*(0.01z-4)}}}
{{{R=4x+0.01zx-4x+0.05z-20)}}}
{{{R=4x+0.01zx-4x+0.05z-20)}}}
{{{R=0.01zx+0.05(z-20/0.05)}}}
{{{R=0.01xz+0.05(z-400)}}}
The term {{{0.01xz}}} represents {{{"x%"}}} of the amount {{{z}}}
The term {{{0.05(z-400)}}] represents an extra {{{"5%"}}} of the {{{z}}} in excess over {{{400}}}
The initial threshold is {{{highlight(400)}}}
{{{z}}} represents the total amount the customer spends in a month
{{{x}}} represent the percentage of rebate for purchases up to {{{400/month}}}
Any excess over that {{{400}}} threshold of monthly expenses results in an additional {{{"5%"}}} rebate.