Can u help me with this

acc to quesperimeter of figure= 3a^2+15a+9

let missing dimension be x

= x+10a-2+a^2-7+5a=3a^2+15a+9

x+15a+a^2-9=3a^2+15a+9

x=2a^2+18

step-by-step explanation:

ok so im not 100% sure but you would start by adding 5.1t and 1.9t beacuse they have the same variable. that is 7t.   then add -3.6 + 1.2 which is -2.4

so then keep that as -2.4 + 7t. i apologize if this is incorrect. best luck on your test < 3