Question 12244
This one seems confusing at first, but you just need to get the two r terms together so you can factor them out, here is how I did the problem
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{{{ S = (rL-a)/(r-1) }}} Mulitply (r-1) to get it out of the denominator
{{{ (r-1)S = rL-a }}} Distribute the S through r-1
{{{ rS - S = rL - a }}} now we need to get both r terms on one side of the equation so we can take the GCF of 'r' out
<LI> so we subtract rL from both sides
<LI> add S to both sides
{{{ rS - rL = S - a }}} Factor out the r on the left
{{{ r(S - L) = S - a }}} Divide both sides by S - L
{{{ r = (S-a)/(S-L) }}}

Hope that helps, Mr. C