there are 16 boxes total, and 45 wheels total.
we know that each bicycle/tricycle is in it's own box.
i'm going to use the variable "b" for bicycle and "t" for tricycle
b + t = 16
(because b is the amount of bicycles and t is the amount of tricycles)
now we know that there are 45 wheels total.
there are 2 wheels for a bicycle and 3 wheels for a tricycle
2b + 3t = 45
now we have a system of equations
b + t = 16
2b + 3t = 45
You can solve this multiple ways, but I'm going to use substitution.
b + t = 16 can also be written as b = 16 - t (if you subtract both sides by t)
then we can substitute this b = 16 - t into the other equations
2(16 - t) + 3t = 45
32 - 2t + 3t = 45
32 + t = 45
t = 13
now you can plug that back into the original equations
b + 13 = 16
b = 3
2b + 3(13) = 45
2b + 39 = 45
2b = 6
b = 3
If you have any more questions, feel free to ask!