Box A contains 10 pens that are either red or blue in colour. Box B contains 23 pens that are also either red or blue in colour.
The number of blue pens in Box B is twice the number of blue pens in Box A while the number of red pens in Box B is thrice the number of red pens in Box A. Write a pair of linear equations using b as the number of blue pens in Box A and r as the number of red pens in Box A.