This is for algebra 2. im not sure that im doing it correctly. you!

A)    an = a1 + (n-1)d

so Sn  = (n/2)[ a1 + ( a1 + (n-1)d)]
            = (n/2) [ 2a1 + (n-1)d ]
            =  na1  +  n(n-1) 
                             d
                                2

If jon had $4.00 then takes away $2.25, then he should have $1.75 left. $4.00 - $2.25 = $1.75 hope this ; )