Final answer:
The student's question is not entirely clear, but based on the calculations provided, it involves solving for 'x' in a statistical or algebraic context, possibly dealing with mean values and standard deviations.
Step-by-step explanation:
The student seems to be asking for help with solving for the variable x. However, the question is a bit unclear as it references '21 and 52°' without additional context. Nonetheless, based on the provided calculations, it appears that x represents a central value in a set of statistical calculations or in a mathematical equation. The examples given include basic arithmetic operations and the concept of standard deviation (s), which suggest topics from statistics or algebra.
For instance, the calculated values b. (x + 1s) = 11.25 and c. (x - 2s) = 9.09 imply that x is the mean value, and s represents the standard deviation of a dataset. Similarly, finding x in a series of equations, such as '13 z = 2.78' or '15 x = 20', involves solving algebraic equations to determine the value of x.