The number you seek is 78 - it is a multiple of both 6 and 26 and is less than 85.
To be a multiple of both 6 and 26 it must be a multiple of their lowest common multiple:
6 = 2 x 3
26 = 2 x 13
lcm = 2 x 3 x 13 = 78
So it must be one of 78, 156, 234, ...; only 78 satisfies the criteria of being less than 85.
26
78.
26
13 and 26
since 7 and 26 has no common factors (anyway, 7 is a prime number, and 26, on the other hand, is a composite number w/o 7 as a possible factor, nevermind this line if it confuses you ) the smallest common multiple will be 7*26. any other multiple will just be a natural number times the lowest common multiple (7*26)
48 - 26 = 22
23
Note that 26x3=78. Next note that 78 divided by 6 is 13. This tells us 78 has 26 and 6 as factors and clearly it is less than 85.
- sqrt(26)
-sqrt(26)
13 has a multiple of 26
26
- sqrt(26)
78
78
13
1 and 2