Why 122 x 3? You need to know the purpose of each number. You cannot see the first two numbers and immediately do anything to them, because they are not linked directly.

Mrs Ling had 122 sandwiches AT FIRST (not in the afternoon).

She sold 3 times as many sandwiches in the morning as in the afternoon.

She had two sandwiches left.

Your 122 x 3 would have been correct if "Mrs Ling sold 122 sandwiches in the afternoon". But here, it is not the case.

Since Mrs Ling had 122 sandwiches at first and had 2 sandwiches unsold,

Number of sandwiches sold for the day
= 122 - 2
= 120

This is to be divided into the morning and the afternoon.

Since she sold 3 times as many sandwiches in the morning as in the afternoon,

Afternoon = 1 unit
Morning = 3 units

Total = 4 units, which represents the 120 sandwiches sold for the day.

4 units = 120
1 unit = 120 divided by 4 = 30

She sold 1 unit of sandwiches, or 30 sandwiches, in the afternoon.

On Monday, a factory produced 465 shirts.

On Tuesday, it produced 3 times as many shirts as it did on Monday.

These are linked, because on Tuesday it produced 3 times as many as Monday which produced 465 shirts.

So,

Monday = 1 unit = 465
Tuesday = 3 units = 465 x 3 = 1395

Total number of shirts produced on the two days
= 465 + 1395
= 1860