Hello Frank Originally Posted by

**frank9999** ok ill try to explain it again,

i have the following formules:

when i enter a = 30 in the formule above, it will return c = 10238.

now i need a formula where i can

input any type of C value, and it will return the corresponding a value according to the formula used above.

For example i put in c = 10238, it will return a = 30.
Thanks

~ Frank

I understand now what you require - you simply need the inverse formula. However, I do not understand how the formula you have quoted gives $\displaystyle c = 10238$ when $\displaystyle a = 30$.

You have:$\displaystyle b = (a + 650 \times 2\tfrac{a}{5.5}) + (a\times450)$

The part that is unusual is $\displaystyle 2\tfrac{a}{5.5}$. This really means $\displaystyle 2+\tfrac{a}{5.5}$. So when $\displaystyle a = 30$:$\displaystyle b = (30 + 650 \times (2+\tfrac{30}{5.5}))+(30\times 450)$$\displaystyle = 18375.45...$

and this then gives:$\displaystyle c = 4323.86...$

Please clarify what you mean by $\displaystyle 2\tfrac{a}{5.5}$. Once you have done this, we may be able to reverse the formula to get $\displaystyle a$ in terms of $\displaystyle c$.

Grandad