1.

t=total amount

x=amount bought.

after we buy the $4.60 one we add 4.60 to the total and add 1 to the amount bought. this gives us a new average of 1.8

so we just solve for x;

first equation gives t=1.4x plug this into second equation and solve for x. (x=7 not including the one she bought last. so 8 in total)