Answer:
-4
Step-by-step explanation:
[tex]\text {Using slope intercept form and the information provided: }y = 3x + b\\x = -1\\y = - 7\\\\\text{So: }[/tex]
[tex]y = 3x + b \rightarrow -7 = 3(-1) +b[/tex]
Solve for B.
[tex]-7 = 3(-1)+b\\3 * -1 = -3\\-7 = -3 + b[/tex]
[tex]\text {Add 3 to both sides: } -7 +3 = -3(+3) +b\\\\-4 = b[/tex]
Your y-intercept should be -4.