An estimated regression equation has the form: hat$(y)=7-0\mathrm{.}068x_1-0\mathrm{.}5x_2.$ As $x_1$ increases by $1$ unit $($holding $x_2$ constant$),$ then $y$ is expected to

a$.$ Increase by $0\mathrm{.}068$

b$.$ Decrease by $0\mathrm{.}068$

c$.$ Increase by $0\mathrm{.}5$

d$.$ Decrease by $0\mathrm{.}5$