Explanation:
x = number of minutes
35x = number of extra words after x minutes
This is because you add on 35 words per minute (wpm). So for instance, after 10 minutes, you add on 35x = 35*10 = 350 more words.
This is on top of the initial 150 words you already wrote yesterday. So we add the 35x onto the 150 to get the expression 35x+150. This represents the number of words total from yesterday and today combined.
Saying y = 35x+150 shows we have a linear function of the form y = mx+b
m = 35 = slope
b = 150 = y intercept
