Question 568964
Let Mary's age be {{{x}}}.
She cuts {{{x}}} flowers the first day, {{{2x}}} flowers the second day, {{{4x}}}the third day, {{{8x}}} the fourth day and {{{16x}}} the fifth day.
The numbers of flowers cut each day form a geometric sequence (or geometric progression), but we do not care about that until Algebra 2 (in the USA).
What's important is that on the fifth day she cut {{{16x}}} flowers and that number is the same as her grandmother's age plus Mary's age: {{{60+x}}}. So
{{{16x=60+x}}} --> {{{16x-x=60+x-x}}} --> {{{15x=60}}} --> {{{15x/15=60/15}}} --> {{{highlight(x=4)}}}