Answer:
Heather served 10 orders.
Felipe served 30 orders.
Jim served 50 orders.
What we know:
Let's refer to each person by their first initial (H, J, & F)
H + J + F = 90
F = 3 * H
J = 5 * H
Substitution:
Let's replace F and J by their equivalents in relation to H (basically making the entire left side only H)
H + (5 * H) + (3 * H) = 90
H + (5H) + (3H) = 90
9H = 90
H = 90/9
H = 10
Final Calculations
Now that we know how many orders Heather served, we can calculate how many Jim and Felipe served
F = 3 * H
F = 3 * 10
F = 30
J = 5 * H
J = 5 * 10
J = 50
