If there's only 1 table, then you need 5 roses total (5*1 = 5)
If there are 2 tables, then you need 10 roses total (5*2 = 10)
If there are 3 tables, then you need 15 roses total (5*3 = 15)
If there are 4 tables, then you need 20 roses total (5*4 = 20)
At this point, you probably see the pattern: you multiply 5 by the number of tables to get the total number of roses. So it would look like this equation
(number of roses) = 5*(number of tables)
r = 5*x
where r is standing in for "number of roses" as shorthand; also, x is standing in for "number of tables".
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Final Answer: r = 5x (lower right corner choice)
Note that 5*x is the same as 5x (both of which mean "5 times x)
