Calculation:

The congruence is \(18 \equiv 60\ mod\ 7\).

Consider \(\frac{18-60}{7}\),

\(\frac{18-60}{7} = -42/7 = -6\)

Because —6 is an integer, \(18 \equiv 60\ mod\ 7\) is a true congruence.

Hence, the congruence \(18 \equiv 60\ mod\ 7\) is true.

The congruence is \(18 \equiv 60\ mod\ 7\).

Consider \(\frac{18-60}{7}\),

\(\frac{18-60}{7} = -42/7 = -6\)

Because —6 is an integer, \(18 \equiv 60\ mod\ 7\) is a true congruence.

Hence, the congruence \(18 \equiv 60\ mod\ 7\) is true.