If P denotes '+', Q denotes '-', R denotes '÷', S denotes 'x' and 28P8R4Q3S1=…

To determine the value of a, we must first replace the letters with their corresponding mathematical operations and then apply the correct order of operations (BODMAS/PEMDAS).

Step-by-Step Analysis
Define the Substitutions:

P = +

Q = -

R = / (division)

S = * (multiplication)

Substitute into the Expression:

Original: 28 P 8 R 4 Q 3 S 1 = a³

Substituted: 28 + 8 / 4 - 3 * 1 = a³

Apply Order of Operations (BODMAS):

Division: 8 / 4 = 2. The expression becomes 28 + 2 - 3 * 1 = a³.

Multiplication: 3 * 1 = 3. The expression becomes 28 + 2 - 3 = a³.

Addition and Subtraction (left to right): 28 + 2 = 30, and 30 - 3 = 27.

Therefore: 27 = a³.

Solve for "a":

Since 3 * 3 * 3 = 27, then a³ = 27 implies a = 3.