Hi, secondary maths teacher here. I'll try to get this right

Three pairs of shoes = 30. Therefore single shoe is 30/6 = 5

Two boys plus pair of shoes = 20. We have already established single shoe = 5, so pair of shoes = 10. This means two boys = 20 - 10.

So boy is 10/2 = 5

Four bags of chips plus a boy = 13. We have already established that a boy = 5. Therefore two pairs of double chips = 13 - 5.

So 4 bags of chips = 8 4. So single chips = 2

Now it's time to think about BIDMAS and Algebra.

BIDMAS (BODMAS)

Brackets - we have none

Indices (Orders) - we have none

Division and Multiplication are simultaneous but we only have Multiplication

Addition and Subtraction are simultaneous but we only have Addition

Algebra - when we put two terms next to each other with no operation sign (add, subtract, multiply or divide) between them, they are deemed to have multiplied by each other.

So this should work out as

Shoe + boy x pair of shoes x two bags of chips x bag of chips

If we substitute the values back in, we get

5 + 5 x 10 x 4 x 2

and if we simplify this into the value for each symbol (shoe, dressed up boy with chips, chips) it becomes

= 5 + 200 x 2

= 5 + 400

= 405