Question 1025811
Find first the equation for Line_1.

Two points on Line_1 are (0,9) and (4,7).
Slope is  {{{(7-9)/(4-0)=-2/4=-1/2}}}.
Equation for Line_1 is  {{{y=-(1/2)x+9}}}.


The question of finding gradient of Line_1 reads like you want the slope;
which is now found, {{{-1/2}}}, for LINE_1.


The slope of Line_2 is the negative reciprocal of  that of line_1 because these
two lines were given as perpendicular, so Line_2 has slope {{{2}}}.