Question 871866
(1):
x and y, the angle measures.
Description becomes translated to these:


{{{highlight(x+y=90)}}}, and {{{highlight(y=12+5x)}}}, and this is using x<y.  The red-highlighted equations is your system.




(2):

Let x and y be Ellie and Kay age now.
IN SEVEN YEARS, your description becomes {{{(x+7)+(y+7)=20}}}; and your first part is, for "now", {{{highlight(x=2y)}}}.
The age sum equation is simplifiable to x+y=20-14, or {{{highlight(x+y=6)}}}.  You should be able to see how to solve this now that two equations in two unknowns are formed.