Cohort Retention — Month-Over-Month Return Rate

You're a customer-success analyst computing month-over-month retention for the early-2026 cohorts. The 17-row transactions table (columns A–F) already has two engineered helper columns:

• A–D: TxID, CustomerID, OrderMonth (Jan/Feb/Mar/Apr), Amount
• E (IsFirstOrder): 1 on each customer's first-ever order, 0 on later orders
• F (ReturnedNextMonth): 1 if (a) this row is the customer's first order and (b) the same customer placed another order in the very next month — 0 otherwise

The cohort labels are pre-populated in column G (G2=Jan → G5=Apr) and the Retention Rate header sits in H1.

Retention rate per cohort:

retention(cohort) = (count of cohort customers who returned next month) / (cohort size)

• cohort size = count of first-orders that occurred in cohort_month
• returned = count of those first-orders where ReturnedNextMonth = 1

Your task:

1. In column H (Retention Rate), write a single formula using LET + SUMIFS that:
   • binds the data ranges to readable names,
   • computes n (cohort size) and retd (returned count) by filtering on OrderMonth = cohort,
   • returns retd / n, falling back to 0 when n = 0 so the formula is safe to drag past the data.
2. Drag-fill from H2 → H5.

Graded cells: H2 (Jan → 0.75), H4 (Mar → 0.25), H5 (Apr → 0).