Solution: If the unit price of type A envelope is A, the unit price of type B envelope is a-2.
If you buy B-type A envelopes, you will buy 30-b-type B envelopes.
1 yuan.50 = 150.
ab= 150( 1)
(a-2)(30-b)= 150(2)
By (2)
30a-60-ab+2b= 150
Substitution (1)
30a- 150+2b=2 10
30a+2b=360
15a+b= 180
b= 180- 15a
Replace (1)
a( 180- 15a)= 150
Answer? - 12a+ 10=0
(a-6)? =36- 10
a-6= √26
a=6 √26
A 1≈ 1 1 min, then the b-type envelope 1 1-2=9 points.
A2≈0.9, then 0.9-2=- 1. 1 of the type B envelope is irrelevant, so it is discarded.
The unit price of type A is 1 1, and that of type B is 9.