According to the meaning of the question

65k+b = 55； ...............( 1)

75k+b=45....................(2)

Solution, k =-1; b = 120；

The function expression is: y =-x+120;

2)、

According to the meaning of the question; Let the sales unit price be X yuan;

(-x+ 120)(x-60)= 89 1；

Simplify,

x？ - 180x+809 1=0

(x-87)(x-93)=0

Solution, x1= 87; x2 = 93

After investigation, x 1=87 is true, and the profit rate =(87-60)÷60=45% (in line with the meaning of the question).

When x2=93, the profit rate =(93-60)÷60=55% (irrelevant).

Pricing 87 yuan.