Verified answer

Any line

Y = m*X + b

we replace the points

1)

-7 = m * (-6) + b

b = 6m - 7

2)

13 = m * (8) + b

13 = 8m +b

we replace 'b' from 1)

13 = 8m + (6m-7)

13=8m+6m-7

20=14m

m=10/7

we replace m in 1) or 2)

13=8 * (10/7) + b

13=80/7 + b

b=11/7

so the function is

Y = 10X/7 + 11/7