Answer:
2
Step-by-step explanation:
So we have the equation:
[tex]7a+1+3=18[/tex]
Add 1 and 3:
[tex]7a+4=18[/tex]
Subtract 4 from both sides:
[tex]7a=14[/tex]
Divide both sides by 7:
[tex]a=2[/tex]
And we're done!
