Given:
The cost of a black printer ink cartridge is $16.99.
The cost of a colour printer ink cartridge is $21.99.
A total of 47 of these cartridges were sold for a total of $908.53.
To find:
The number of items sold in each type.
Step-by-step explanation:
Let x be the number of a black printer ink cartridge.
Let y be the number of a colour printer ink cartridge.
According to the question,

Multiplying 16.99 in equation (1), we get

Subtract (3) from (2), we get

Substitute in equation (1) we get,

Thus,
The number of a black printer ink cartridge is 25.
The number of a colour printer ink cartridge is 22.
Final answer:
• The number of a black printer ink cartridge is 25.
,
• The number of a colour printer ink cartridge is 22.