a ) S 1 + S 2 = 90 → S 2 = 90 − S 1 b ) 90 + S 3 3 2 = S 1 c ) S 3 3 2 = S 2 → 3 2 ∗ S 2 = s 3 {\displaystyle {\begin{aligned}&a)S_{1}+S_{2}=90{\color {blue}\rightarrow S_{2}=90-S_{1}}\\&b){\frac {90+S_{3}}{\frac {3}{2}}}=S_{1}\\&c){\frac {S_{3}}{\frac {3}{2}}}=S_{2}{\color {blue}\rightarrow {\frac {3}{2}}*S_{2}=s_{3}}\\\end{aligned}}}
b ) 90 + S 3 3 2 = S 1 c ) 3 2 ∗ S 2 = s 3 a ) S 2 = 90 − S 1 ↓ 90 + 3 S 2 2 3 2 = S 1 2 ( 2 ∗ 90 + 3 S 2 2 ) = 3 S 1 2 ∗ 90 + 3 ( 90 − S 1 ) − S 1 60 + 90 − S 1 = S 1 2 S 1 = 150 ↓ S 1 = 75 k m h r S 2 = 90 − 75 = 15 k m h r {\displaystyle {\begin{aligned}&b){\frac {90+S_{3}}{\frac {3}{2}}}=S_{1}\\&c){\color {blue}{\frac {3}{2}}*S_{2}=s_{3}}\\&a){\color {blue}S_{2}=90-S_{1}}\\&\downarrow \\&{\frac {90+{\frac {3S_{2}}{2}}}{\frac {3}{2}}}=S_{1}\\&2({\frac {2*90+3S_{2}}{2}})=3S_{1}\\&2*90+3(90-S_{1})-S_{1}\\&60+90-S_{1}=S_{1}\\&2S_{1}=150\\&\downarrow \\&S_{1}=75{\frac {km}{hr}}\\&S_{2}=90-75=15{\frac {km}{hr}}\\\end{aligned}}}