What is the value of a in the equation 3 a + b = 54, when b=9

To solve this plug in 9 for b and solve for a like so...

3a + 9 = 54

9 must be combined with 54. To do this you must subtract 9 from both sides. This will cancel out 9 from the left and bring it over to the right

3a + (9 - 9) = 54 - 9

3a + 0 = 45

3a = 45

Now we must isolate the a. To do this you have to divide 3 to both sides. This will make 3 on the left side 1 and bring 3 over to the other side

3a/3 = 45/3

1a = 15

a = 15

Hope this helped!

~Just a girl in love with Shawn Mendes