Can both number be negative? if yes give an example

Yes they can.
for example if you have - 7 + - 8=- 15 the rule for adding/subtracting is that when you have two negative you add and keep the negative sign. When you multiply/divide the two negative makes the answer become positive for example - 5 × - 7 = 35 or when you divide - 6 ÷ - 3 = 2.