ive been stuck for a hour help please

Let v be speed in km/hr on outward journey.

Outward time:  10/v hr

Return time: 10/(v - 3) hr

Total time:  10/v + 10/(v - 3) = 7

Can you take it from here?
 

\(x = {v*t}\)

V_{i = initial velocity}

T_{f = second time}

Ti _{= first time}

\(10= {Vi* Ti}\)

\(10 = {(Vi-{3km\over h}(tf))}\)

\(Vi*Ti= {(Vi- { 3km\over h}})*tf\)

\(Tf = {7h-Ti}\)

\(Vi*Ti = (Vi-{3km\over h})*(7h-Ti)\)

\(Vi*Ti = ({Vi*7h-ViTi-{3km\over h}}+{3km \over h}*Ti)\)

\(Vi*Ti= {7h*Vi - 21km + {3km\over h}}*Ti\)

\(20km = {7h*Vi - 21km +{ 3km\over h}}*Ti\)

\(41km ={ {70km*h+ { 3km\over h}}*Ti^2\over Ti}\)

\(41km ={ {7h*10km \over Ti}+{3km*Ti\over h}\over Ti}\)

\(0={ {3km*Ti^2\over h} - 41km*Ti+70 km*h }\)

\(0 = {3x^2 -41 x + 70 }\)

_{This equation gives us two answers:}

_{2 = the number of hours in the initial trip}

_{How fast did she walk going out to the country?}

\(5km\over h\)