Hey there!
To start, first let's assign a variable to each person:
A to represent the miles biked by Albert
B to represent the miles biked by Bob
Now, let's set up a system of equations:
A=3B
A + B = 72
Next, use substitution (plug 3B in for A in the second equation since A is equal to 3B):
3B + B = 72
Then, simplify and solve:
3B + B = 72
(combine like terms)
4B = 72
(divide both sides by 4)
B=18
Now that you know the amount that Bob biked, you can plug his miles into the equation for Albert: A=3B
B=18
A=3(18)
A= 54
Your final answer would be that Albert biked 54 miles.
Hope this helps!