Calculate the size of $\angle ABC$∠ABC.
In the following figure, $\angle RTV$∠RTV=$49$49° and $\angle UTV$∠UTV=$26$26°. Find $\angle RTU$∠RTU.
Solve problems involving the addition, subtraction, and multiplication of whole numbers, using a variety of mental strategies (e.g., use the commutative property: 5 x 18 x 2 = 5 x 2 x 18, which gives 10 x 18 = 180)