Answer :

crisforp
2) 
a*2 + b = 26;
a*(-4) + b = -16;
then, a*6 = 42 => a = 7 => b = 26 -14 => b = 12;

from table, 7*9 + 12 = 63 + 12 = 75, correct;
                7*(-8) + 12 = -56 + 12 = -44, correct;

slope = ( -44 + 16) / ( -8 + 4) = ( - 28) / (-4) = 7 = a;