Using only the addition and multiplication operations with the numbers 1, 2, 3, and 4 each exactly once,it is possible to build a numeric expression (with parentheses to show the order used to build theexpression) that evaluates to 21. For example, 1 + ((2 + 3) · 4) is one such expression.a. Build two more numeric expressions that evaluate to 21 using the criteria above. Both must bedifferent from the example given.b. In both of your expressions, replace 1 with a, 2 with b, 3 with c, and 4 with d to get two algebraicexpressions. For example, a + ((b + c) · d) shows the replacements for the example given.