Let's assume that number as x
The product of 7 and a number =7x
and then increased by 1
so, it will become
=7x+1
now, it is between 15 and 43
so, we can write as

now, we can solve for x
Since, we have to isolate x
step-1:
Subtract all the sides by 1


step-2:
Divide all the sides by 7


so, solution is
.............Answer