Help me, please! It's due tomorrow!

m=y2-y1 / x2-x1

m=15-20 / 1-0

m=-5 / 1

m=-5

y=mx+b

20=-5*0+b

20=0+b

20=b

y=-5x+20

i believe it's a.

i'm not sure on this one, most likely correct.

answer: 8 years

step-by-step explanation:

the explanation is that in 8 years the child will be 20 and in 8 years the father will be 40 and 20 is half of 40.