<s>[INST] Formula help with this equation I don't know what the answer to this formula is, can someone please help me.
I've tried lots of things but getting no where.
If $x=\dfrac56+\dfrac{15}{18}-\dfrac{10}{12}$, then $(x-1)3=$ ?
 [/INST] The expression $x=5/6+15/18-10/12$ may be simplified considerably:
\begin{align*}
x &= \frac{5}{6}+\frac{15}{18}-\frac{10}{12}\\
&= \frac{5}{6}+\left(\frac{30}{36}-\frac{30}{36}\right)\\
&= \frac{5}{6}.
\end{align*}
Thus, $x-1=-\frac{1}{6}$ and $3(x-1)=-\frac{1}{2}$. 
As @ParthKohli has pointed out in a comment, you may actually be interested in the expression $(x-1)^3$, rather than in $(x-1)3$. If that's the case, you can still use the simplification for $x$ provided above to obtain
$$(x-1)^3=-\frac{1^3}{6^3}=-\frac{1}{216}.$$
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