Answer:
x = 115 - p
Step-by-step explanation:
generally in algebra you will use the letter "x" to represent a value you do not know, so it wants an algebraic expression for "p subtracted from 115", this can be rewritten as 115 - p. So the unknown value "x" is equal to 115 - p.
Step-by-step explanation:
Given

3a + b = 54...when b = 9
3a + 9 = 54
3a = 54 - 9
3a = 45
a = 45/3
a = 15 <===