(6 points)Let the following relation schemas be given:
R = (A, B, C)
S = (D, E, F)
Let relations r(R) and s(S) be given. Give an expression in SQL that is equivalent to each of the following queries.
a. s B = 4 AND A>2500 (R)
b. PA, D (s D=500 AND A=F (R ´ S))