The letters of the alphabet are numbered $a=0,\ b=1,\ {\rm to}\ z=25$ and each pair of letters is replaced by a pair of numbers. There are $26\times 26=676$ pairs of numbers. It is possible to store the codes for all 676 pairs and look them up as needed but much more efficient to use a decyphering formula.
Each pair of numbers $(\alpha, \beta)$ is encoded as another pair of numbers $(\alpha',\beta')$ where $$\alpha' = \alpha + 3\beta \pmod {26}$$ $$\beta' = 5\beta \ \ \pmod{26}$$ Find $\alpha$ and $\beta$ in terms of $\alpha'$ and $\beta'$ and hence decode the following quotation which is a remark made by Einstein: