Roberto studied 3/5 hour every day for 7 days. how many hours did roberto study in 7 days?

Let me explain how you do this 
if for 1 day he studies 3/5s of an hour. And the question is asking for 7 days then all we have to do is multiply 3/5s times 7! Ill guide you through the math;)
 3                                                               3         7    
  x   7  we can also write it like this   ---   x   ---   lets use this one:)  
 5                                                               5         1

but now our next step is to multiply across!
 
 3         7   =   3 x 7 = 21 
---   x                         so our new fraction i
 5         1   =   5 x 1 = 5 

 21
  and since 5 goes into 21 four times and 2 is left over this is how         5     much he studied in 7 days  4.2 hours
or as a fraction...
    1
4
    5
answer? 4.2 hours studied :D
have a good one and 
MARK ME BRAINLIEST!!:D
thxx bye