Question 1151412

Solution, with assumptions...

<pre>
For Mermaid, 7hrs costs:
{{{ w = 7(25)+40 = 215 }}}

For Dolphin, we need to figure out the formula they use:
ASSUMING it is of the form f(h) = c*h + k   (h in hours, k is a constant, say
a sign-up fee)

From the given cost info:
  f(2) = c*2 + k = 110
  f(4) = c*4 + k = 155
 (we don't need f(6) for this, but it can be used to check the formula
  we're about to derive)

solve these last two equations (one way: subtract f(2) from f(4)):
        2c = 45 -->  c=22.5  --> (using f(2) for example): k=65

For Dolphin, we have f(h) = 22.5*h + 65
[ check using f(6):  22.5*6 + 65 = 135 + 65 = 200 ]

{{{ f(7) = 22.5*7 + 65 = 222.50 }}}

Dolphin costs $222.50 for 7hrs of lessons, while Mermaid costs $215.00 for 
7hrs of lessons, or $7.50 less than Dolphin.