Question 101818
T=ma+b
First, state what you know from the data. Equation (1) uses the data from Banff. 
(1) 95 = m(1383)+b
Equation (2) uses the data from Mt. Logan. 
(2) 80 = m(5951)+b
Good news. Two equations, two unknowns, there is a solution. Use one equation to solve for b and then substitute into the other equation to solve for m. 

Let’s use equation (2) and solve for b. 
(2) 80 = m(5951)+b
80 = m(5951)+b
80-m(5951) = m(5951)-m(5951)+b Additive inverse of m(5951) or (-m(5951))
80-m(5951) = b or
(3) b = 80-m(5951) We’ll call this equation (3) but it’s really (2) re-arranged. 

Use this in equation (1) and solve for m.
(1) 95 = m(1383)+b
95=m(1383)+(80-m(5951))
95=m(1383)-m(5951)+80 Simplify
95=-4568m+80
95-80 = -4568m+80-80 Additive inverse of 80 or (-80).
15=-4568m
15/(-4568)=-4568m/(-4568) Multiplicative inverse of -4568 or (1/-4568).
-15/4568 = m or
m = -15/4568

Substitute this value into (1), (2), or (3) to solve for b. Equation (3) is the most direct. 

(3) b = 80-m(5951)
b = 80 – (-15/4568)(5951)
b = 80 + (15/4568)(5951)
b = 80 + (89265/4568)

Those are the exact solutions. Approximately the solutions are m = -.00328 and b= 99.5. Therefore your equation becomes T=-.00328A + 99.5. Double-checking by using your original values T(1381) = 95.0 and T(5951) = 80.0. These values match your data values so m and b are correct. 
m=-.00328, b=99.5