Aherd of zebra currently has 45 members. based on the available resources, biologists estimate that the size of the herd will increase at a rate of 7% per year. which of the following graphs models this relationship, if the x-axis represents years and the y-axis represents number of zebra?

In this case, the zebra growth will increase 7% every year which means the growth will increase every year since its count from total population.  When there is increased in growth, that will make the graph not linear. 
With x-axis represent year and y-axis represent number of zebras, the graph will quadratic graph ( U-shape)