Monitoring well $2$has an elevation at surface $($masl$)$of $145$m$,$a depth of piezometer of $65$m$,$and a depth to water of $17$m below ground surface. Monitoring well $3$has an elevation at surface $($masl$)$of $145$m$,$a depth of piezometer of $23$m$,$and a depth to water of $12$m below ground surface.What is the vertical hydraulic gradient between the two monitoring wells?