How much will Sancia earn when she works 3 hours at time-and-a-half and 4 hours at double time? Her normal pay is $\$ 21.80$ per hour.

Step 1 ：Let's find the pay for time-and-a-half and double time hours separately:

Step 2 ：Time-and-a-half pay: \(3 \times 1.5 \times 21.80 = 98.10\)

Step 3 ：Double time pay: \(4 \times 2 \times 21.80 = 174.40\)

Step 4 ：Add the two amounts to find the total earnings:

Step 5 ：\(98.10 + 174.40 = 272.50\)

Step 6 ：\(\boxed{272.50}\)