math
posted by Jeffery on .
On Saturday, Alberto filled his right rear tire with air at the gas station around the block from where he lives. Three days later the tire pressure in that tire measured 26 psi (pounds per square inch). On the following Saturday, one week after he had originally filled the tire has been losing tire pressure at a constant rate since he filled the tire
What is the expression to solve for b

no idea what "b" represents.
And with only one data point, we cannot determine anything else. What was the starting pressure? Or, how much pressure did it lose each day?
Please make sure your posting accurately reflects the problem as presented, maybe with some mention of additional context, if any, as in the case of followup problems in a set. 
Alberto filled his tire on a Saturday. Three days later the tire pressure in the tire measured 26 psi. On the following day one week after he had originally filled the tire, the tire pressure measured 18 psi.
I'm to to find b in y=2x+b
I'm trying to solve the equation for b and substitute that value into the expression. 
we have two points: (3,26) and (7,18)
You are correct that y = 2x+b
So, plug in either point. For example,
26 = 2(3)+b
26 = 6+b
b = 32
y = 2x+32 
I am still having difficulty finding the expression