SOLUTION: The number of bicycles in a repair shop is 7 time the number of tricycles in the shop. There are 221 wheels in the repair shop. How many bicycles are in the shop? # B's = 7 * #

That's correct, so just write that as:

B = 7T

That's correct so

So # T's TIMES 3 = # T-wheels 

write that as 3T

and

# B's TIMES 2 = # B-wheels

Write that as 2B

Then read this:

There are 221 wheels in the repair shop

And write

2B + 3T = 221

So you have these two equations:

B = 7T
2B + 3T = 221

Since B equals 7T from the first equation, put (7T) in place of
B in the second equation:

2(7T) + 3T = 221

Simply 2(7T) as 14T and replace 2(7T) by 14T

14T + 3T = 221

Add the like terms 14T plus 3T and get 17T, so put 17T
in place of 14T + 3T:

     17T = 221

Divide both sides by 17

     = 

Cancel the 17s on the left sides of the equal sign:
Divide 221 by 17 on the right:

    T = 13

So there are 13 tricycles.

Now go back to the equation:

    B = 7T

and now that we know that T = 13, we substitute (13)
for T

    B = 7(13)

Then we multiply 7×13 and get 91

So there are 91 bicycles, and 13 tricycles.

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Checking:
The 91 bicycles have 91×2 or 182 wheels.
The 13 tricycles have 13×3 or 39 wheels.
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                     Total = 221 wheels.

That checks, so we are correct.

Edwin