Question 19390
All these problems are essentially the same.
You have quantity data regarding number of different kinds of coins.
And you have value data: e.g. x nickels are worth 5x cents.
 
Look at your problem #1.
Read it carefully.  Look for quantity information.  Look for value information.
The quantity info. indicates there are fewer dimes than quarters.
Let the number of dimes by "x".
Then number of quarters is "x+4"
The value of the dimes is 10xcents
The value of the quarters is 25(x+4)=25x+100
Equation:
 The $2.05 is a value idea.
Value of dimes + Value of quarters is 205cents
     10x + 25x+100 = 205
          35x  = 105
            x  = 3 (# of dimes)
          x+4  = 7 (# of quarters)
Try these ideas on your other two problems.  Maybe you can
work them out yourself.

Cheers,
Stan H.