OK so let x be time in minutes and let y be heart rate [per minute].

Let's make a line that goes through (2,82) and (3,86).  First off, you know 
that the slope must be 4/1 because the slop is difference in y divided by 
difference in x, or (Y1-Y2)/(X1-X2). 
The difference in y is 4 and in x is 1, so slope must equal 4/1, or 4.  Our equation so far is:

Y=MX+B  we know it's that format because it is a line.

Y=4X+B  we know m=4 because m is the slope.



What is b?  to find out, let's replace y and x with actual numbers.  These can be 82 and 2 or 86 and 3 [respectively], 
you will get the same answer:
82=4(2)+B
82=8+B
74=B
let's try the other pair:
86=3(4)+B
86=12+B
74=B
Our equation now yields:
Y=4X+74.
Let's replace Y (heartrate) with h and X (minutes) with m as instructed to get
h=4m+74

wooooo!  ok now let's assume 10 minutes, or m=10
h=4(10)+74
h=40+74
h=114
his heartrate will be 114 if he excercises for 10 minutes.

A.)H=4M+74
B.)114 beats per minute