When testing this hypothesis, what is the test statistic

The following regression equation is based on the analysis of four variables:  SM_DOLLARS is the dollar amount of a watershed conservation agency's weekly spending on social media ads.  RADIO_ADS is the number of radio advertisements aired weekly by the agency.  WS_DOLLARS is the dollar amount of the agency’s weekly spending on web search ads.  The variable WEB_VISITS is the number of weekly visitors to their educational website.  These data have been recorded every week for the past three years.   WEB_VISITS (expected) = 208 + 1.5*SM_DOLLARS + 0.5*RADIO_ADS + 0.8*WS_DOLLARS   The data meet the assumptions for regression analysis, and the regression results, including the coefficients, were found to be statistically significant. How many additional weekly web visits would you predict when the agency increases its weekly spending on social media ads by $108 without changing the amount spent on radio ads or web search ads? (Round your answer to the nearest whole number.)

Define linear regression?

Imagine that you, a social psychologist, study people living with HIV. You are interested in the relationship between viral load, the amount of HIV in a sample of blood, and perceived stigma, the amount people with HIV perceive others to hold stigmatizing views about their condition. You have 100 people with HIV complete a perceived stigma scale, as well as provide a sample of blood, so their viral load can be measured. You run a regression analysis using the data you’ve collected to see whether perceived stigma can be predicted based on viral load. The output from the analysis is presented below: How much does the estimate of perceived stigma change if viral load increases by one unit?