Write relational algebra queries for the two specifications below using the relations also defined below:

a. retrieve the names of customers who have ordered parts costing less than $150.00.

b. retrieve the names of customers and the partname of orders with a qty greater than 10.

parts(pno, pname, qoh, price, olevel)

customers(cno, cname, street, zip, phone)

employees(eno, ename, zip, hdate)

zip_codes(zip, city, state)

orders(ono, cno, eno, received, shipped)

odetails(ono, pno, qty)

where qoh stands for quantity on hand and olevel stands for (re)order level. the p, c, e and o single letter prefixes for attributes refer to the parts, customers, employees and orders relations, respectively. the other attribute names are self-explanatory.