He can conclude that the system of equations has no solution since one equation in it always results with false equivalency.
Hope this helps.
r3t40
5x5 - 10x = 0
5x5 - 10x = 5x • (x4 - 2)
Number Properties: PEMDAS
Parentheses, Exponents, Multiplication, Division, Addition, & Subtraction

1. Parentheses

There Are No Exponents, Multiplication, Division, Or Addition
2. Subtraction
Since the rate of the other store is not given, let us just get the sales price of the skirt Dima bought from the discount store.
Original price : $54
Discount rate : 30%
$54 x 30% = $16.20 value of the discount
$54 - 16.20 = $37.80 discounted price.
Since Dima's friend told her she could have had a better deal at a different store, this means that the discount rate is higher than 30%. Let us assume that the discount is 35%
$54 x 35% = $18.90 value of the discount
$54 - 18.90 = $35.10 discounted price.
Discount store: $37.80
Different store: $35.10
Different store sales price is cheaper by $2.70