Maths question 10 marks!!!

Let X be the original selling price of the shoes,

Two weeks ago, she save (40%)X

Last week, she saved 80%(1-40%)X = 80%(60%)X=(48%)X

This week, the shoes on sale=(1-10%)X = (90%)X

(40%)X+(48%)X+12=(90%)X
12=(2%)X
X=600

Therefore, the original selling price of the shoes is $600

assume the original selling price is Y

the first step
My plans to buy a pair of shoes, she saved 40% of the selling price,
hence,
Y x 40% = 0.4Y

and then, she saved 80% of the rest;
the rest is 0.6Y, hence
0.6Y x 80% = 0.48Y

now, the shoes are on sale at a 10% discount.
hence,
Y x 90% = 0.9Y

but she still owns $12, hence
0.4Y+0.48Y+$12 = 0.9Y
0.88Y + $12 = 0.9Y
0.02Y = 12
Y = 600

Hence, the original selling price of the shoes is $600.