step by step explanation
Adding the next term is the concept to solve this type of problems
4+1=5
5+3=8
8+7=15
15+15=30
30+y=x
Now let's look at the series 1,3,7,15,y
1×2+1=3
3×2+1=7
7×2+1=15
15×2+1=31
y=31
Then X=30+y
X=30+31
X=61
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