Change model

How could I modify below equation to create a new model that allows for the effect of the age of the woman on fertility to be different depending on whether the woman lives in an urban or rural area. And also how I could use the parameters of the model and write out the null and alternative hypotheses for the null hypothesis that effect of the age of the woman on number of children is the same in urban and rural areas.
children=B0+ B1 age+ B2 age squared + B3spirit+ B4 protest+ B5 catholic + B6urban+B7 educ+ B8 electric + B9((deuc-7)*electric)+ui

variable name type format label variable label
children byte %8.0g number of living children
age byte %8.0g age in years
spirit byte %9.0g =1 if religion == spirit
protest byte %9.0g =1 if religion == protestant
catholic byte %9.0g =1 if religion == catholic
urban byte %8.0g =1 if live in urban area
educ byte %8.0g years of education
electric byte %8.0g =1 if has electricity