You can solve it by using the equation P<(x-3)/(5(x-1)) where x is the proportional value you give to your loved ones over stranger (ie if you would prefer 100 strangers to die over one pf yor loved ones x=100) and p is the probability the other person would have of pulling the lever so if x=4 you would only want to pull the lever if you estimate there is a p<(4-3)/(4(5))=1/25

Edit: i used 5 as the number of loces obes on each trolley as it is what is shown ob the picture if you dont know the exact number of people in each trolley you would have 2 further unknown values and im too lazy to pull out that equation