If all of them work together

Olive and Arif can do in $1$ day= $\dfrac{1}{42}$ work

Arif and Fahim can do in $1$ day= $\dfrac{1}{45}$ work

Olive and Fahim can do in $1$ day= $\dfrac{1}{90}$ work

$2\text{(Olive+Arif+Fahim)}$ can do in $1$ day

$=\dfrac{1}{42}+\dfrac{1}{45}+\dfrac{1}{90}=\dfrac2{35} \text{work}$

so, $\text{(Olive+Arif+Fahim)}$ can do in $1$ day

$=\dfrac{2}{35\times 2}=\dfrac{1}{35} \text{work}$

so,

If $\text{(Olive+Arif+Fahim)}$ work together in $\boxed{35}$ days they can finish the work