Answers:
17; 6
Step-by-step explanation:
(1) <em>17 and 51</em>
<em>Factors of 17</em>: 1, 17
<em>Factors of 51</em>: 1, 3, 17, 51
The highest common factor of 17 and 51 is 17.
(2) <em>18 and 48
</em>
Factors of 18: 1, 2, 3, 6, 9, 18
<em>Factors of 48</em>: 1, 2, 3, 4, 6, 8, 12, 16, 24, 48
The highest common factor of 18 and 48 is 6.