Hummm, still not able to understand....
Anyone can simplify for me please...

Not sure if this answer would be accepted...Let me know?

3 wallets = 4 belts
1 wallet = 4/3 belts

7 belts - 150 = 4 wallets
7 belts - 150 = 4/3 belts * 4 wallets --- convert all to belts
7 belts - 150 = 16/3 belts
21 belts - 450 = 16 belts
5 belts = 450
1 belt = 90
1 wallet = 90* 4/3 = 120

1 belt + 1 wallet = 90+120 = 210

1050/210 = 5

So 5 belts and wallets were bought.

①
7 belts cost $150 more than 4 wallets.

Multiply by 3,
21 belts cost $450 more than 12 wallets.


②
Since 3 wallets cost as much as 4 belts,

Multiply by 4 ,
12 wallets cost as much as 16 belts.


③
So we can now say that :

21 belts cost $450 more than 16 belts.
That's 5 belts more.

This tells you that 5 belts = $450
1 belt cost = $450 ÷ 5 = $90

④
So 16 belts cost = $90 x 16 = $1440
And this equals cost of 12 wallets.

1 wallet cost = $1440 ÷ 12 = $120


⑤Equal numbers of wallets and belts are bought.

Group every wallet and belt together as 1 set

Total cost of 1 set = $120 + $90 = $210

⑥
Number of sets that can be bought with $1050

= $1050 ÷ $210
= 5

Number of belts and wallets altogether
= 5 sets x 2 items per set
= 10

Thanks for the efforts

So is there anything you still not understand?