Hello! For this question, you can use the old method of guess and check, but that is quite time consuming, so here I have used a method that is taught in P6 and Sec 1 called algebra. It might look new and strange, but it makes solving the question much shorter.
So you see here, we do not know how many tricycles or bicycles are there, so I gave it a letter to symbolise the unknown number. It can be any symbol you want.
From there, we can work out the solution by following the steps listed above.
Hope this helps and please ask if you have any questions how algebra works! It can be used in many math problems! :)

Hmm, alright, since algebra has not been taught yet, here is another method I was taught back then.
If possible, I would not reccomend guess and check since it takes too much time. This method is shorter as well.
Here we start by assuming all the vehicles in the shop were tricycles, and then seeing how many wheels we would have if that is the case.
Because we started assuming with the tricycles, dividing the difference between the number of total wheels and the difference between bicycle and tricycle wheels will give us the total number of bicycles.
If you start by assuming the number of bicycles, then the division will give you the number of tricycles.
This method can be applied to most guess and check questions.
Hope this was more useful! :)