Question

Marcus bought y movie posters for $3 each. Write an algebraic expression for total amount Marcus spent

Answer 1

Well you would have to multiply 3 by what ever (y) is so if (y) was 5 then you could put the equation many ways but just some ways are 
1) 3(y)=15
3(5)=15
15=15
2)3*y=15
3*5=15
15=15
just two ways and remember what you do to one side you have to do to the other but in this case you leave the right side alone

Answer 2

3y would be an algebraic expression that represents what Marcus spent.
For example:
If he bought 12 posters  then 3(12)=36 would represent the total amount he spent.