​68.
a) [[$ f(x)=5-x$]]​
b) [[$ f(x) = 13x + 9 $]]

69.
a) [[$g(5)=12$]]
b) [[$ f(4) = 1 $]]
c) [[$ h(x) = 2x $]]

70.
a) [[$ f(2) = 2+15 = 17 $]]​​​​
b) [[$ g(2) = 7\cdot 2 = 14 $]]
c)  [[$ h(2) = 2^2 = 4 $]]

71.
a) [[$ f(11) = 3\cdot 11 + 1 = 34$]]​​​
b) [[$ f(8) = 3\cdot 8 + 1 = 25 $]]
c) [[$ f(-1) = 3\cdot (-1) + 1 = 2$]]​​​​​​

72.
​a)
[[$ \begin{align} 6x &= 18 &||& :6\\ x&= 3&& \end{align} $]]​
b)
​[[$ \begin{align} 6x &= 0 &||& :6\\ x&= 0&& \end{align} $]]​

73.
a)
​​[[$ \begin{align} 4x -12 &= 12 &||& +12\\ 4x &= 24 &||& :4\\ x&= 6&& \end{align} $]]​
b)
​[[$ \begin{align} 7x + 33 &= 12 &||& -33\\ 7x &= -21 &||& :7\\ x&= -3&& \end{align} $]]​

74.
​[[$ \begin{align} 2x+1&=10-x &||& +x\\ 3x+1&=10 &||& -1\\ 3x&=9 &||& +x\\ x&=3 && \end{align} $]]​

75.
a)
[[$ f(10) = 13\cdot 10 + 13 = 143 $]]​
V: Matka maksaa [[$143$]] kruunua​

b)
​[[$ \begin{align} 13x+70&=1110&||& -70\\ 13x&=1040&||&:13\\ x&=80 && \end{align} $]]​
V: Rahalla voi matkustaa [[$ 80 $]] km pituisen matkan