A line that includes the points (-1,-2) and (a,-10) has a slope of 4. What is the value of a?​

Equation of slope: (y2-y1)/(x2-x1)
(-10 - -2) / (a - -1)
(-10 + 2) / (a + 1)
(-8) / (a + 1)

set this equal to 4 since the slope is given:
4 = -8/(a+1)
multiply (a+1) to both sides
4(a+1) = -8
distribute
4a + 4 = -8
subtract 4 from both sides
4a = -12
divide both sides by 4
a = -3

ANSWER: a = -3

Subtracting is the opposite of adding

Ican't read this very blury