Answer:
0.3 multiplied m 
Explanation:
Given : An algebraic expression 30% of m.
To find : Write an algebraic expression for the word phrase ?
Solution : 
30% = 30 percent i.e. 

'of' = multiplication (symbol ×) 
m = variable or number m
So, 30% of m is 30% multiplied by m
or 

In word phrase - 0.3 multiplied m