The shape of the graph is very similar to a natural logarithm, which is ln(x). ln(x) has an asymptote at x=0. Shift the graph 3 units to the left and you have the graph of ln(x+3), which has an asymptote at x= -3. Also, when x=0, ln(x+3) is about 1. I think ln(x+3) is the answer. Check this online graph to see if this matches: https://www.desmos.com/calculator/ac1axswddl
