Question 53011
<pre><font size = 5><b>1/2 - x/30 = 3(x + 7)/90.

 1      x     3(x + 7)
--- - ---- = ----------
 2     30        90

2, 30 and 90 will all divide evenly into 90. So 90
is the LCD.

Put 90 over 1 like this with a times sign beside it.

 <font color="red">90
----·
  1</font>

Now stick it before every one of those fraction terms:


<font color="red"> 90</font>   1    <font color="red"> 90</font>    x     <font color="red">90</font>   3(x + 7)
<font color="red">----·</font>--- - <font color="red">----·</font>---- = <font color="red">----·</font>----------
<font color="red">  1</font>   2    <font color="red">  1   </font>30      <font color="red">1</font>      90

Now you can cancel the 2 into the 90 on the left, 
getting 45. You can cancel the 30 into the 90, 
getting 3.  You can cancel the 90's on the right.

 45         3           1    
<font color="red"> <s>90</s></font>   1    <font color="red"> <s>90</s></font>    x     <font color="red"><s>90</s></font>   3(x + 7)
<font color="red">----·</font>--- - <font color="red">----·</font>---- = <font color="red">----·</font>----------
<font color="red">  1</font>   <s>2</s>    <font color="red">  1   </font><s>30</s>      <font color="red">1</font>      <s>90</s>
      1          1              1

Now all the denominators are just 1 and therefore can be
left understood, so we just have this::

             45 - 3x = 3(x + 7)

Now you can finish that, right?

Answer:            x = 4

Edwin</pre>