a) x + y = 30 => y= 30 - x
2x + 3y = 70
2x + 3( 30 - x)=70
2x + 90 - 3x = 70
-x + 90 = 70
-x = 70- 90
-x = -20
x = 20
y = 30 - x = 30 - 20 = 10
y=10
b)
[tex] \sqrt{ \frac{x {}^{2} + y {}^{2} }{3} } = \sqrt{ \frac{20 {}^{2} + 10 {}^{2} }{3} } = \sqrt{ \frac{400 + 100}{3} } [/tex]
[tex] \sqrt{ \frac{500}{3} } = \sqrt{166.6} = 7 \sqrt{85} [/tex]
