I have a $TI30XI$ calculator. The button for fractions is labeled "$A$ $b/c$." You put 1 in the calculator and then press the button and put 3 after. The fraction should display a comma-like thing representing the fraction.

Let John's age be $j$

Let John's sister be $s$

$10s = j$

$j + 8 = 18$

John is currently 10 years old right now. His sister is 1 year old.