What does the a, t, and r stand for in the equation y=a(1-r)t?

Hello i need some with trigonometric substitutions. [tex]\int\limits^a_b {x} \, dx[/tex]

Tabby sells clothing at a retail store, and she earns a commission of 6.25% on all items she sells. last week she sold a pair of jeans for $32.50, a skirt for $18.95, and 2 blouses for $14.95 each. what was tabby's total commission? a $4.15 b $5.08 c $81.35 d $348.60

Which expression is equivalent to -5(3x - 6/7)