Write expressions of relational algebra to answer the following questions using the sequential notation used in the book. Which makers sell both PCs and laptops?

The relation Product The relation PC maker model type model speed ram hd price pc pc pc laptop laptop laptop pc pc 250 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 2114 995 478 649 630 1049 510 320 2.66 1024 2.10 1512 1.42 512 2.80 1024 3.20 512 3.20 1024 2.20 1024 2.20 2048 2.00 1024 2.80 2048 1.86 2048 2.80 1024 3.06 512 770 300 laptop 160 650 770 959 649 529 160 80 pc 1 The relation Laptop 1001 1002 1003 2004 2005 2006 1004 1005 1006 2007 1007 1008 1009 1010 3004 3005 1011 1012 1013 2001 2002 2003 3001 3002 3003 2008 2009 2010 3006 3007 model speed ram hd screen price 240 80 printer printer pc pc pc laptop laptop laptop printer printer printer laptop laptop laptop printer printer 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2.00 1.73 1.80 2.00 2.16 2.00 1.83 1.60 1.60 | 2.00 2048 1024 512 512 1024 2048 1024 1024 512 2048 20.1 17.0 15.4 13.3 17.0 15.4 13.3 15.4 14.1 15.4 3673 949 549 1150 2500 1700 1429 900 680 2300 120 100 80 160 The relation Printer model color type price 99 3001 3002 3003 3004 3005 3006 3007 true false true true false true true ink-jet laser laser ink-jet laser ink-jet laser 239 899 120 120 100 200